Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.82   10.645%   $267.5617   $267.56   $267.55   $267.60  
  Purchase #2 $205.51   13.693%   $233.6505   $233.65   $233.65   $233.70  
  Purchase #3 $96.83   5.834%   $102.4791   $102.48   $102.50   $102.50  
  Purchase #4 $198.81   12.212%   $223.0887   $223.09   $223.10   $223.10  
  Purchase #5 $165.71   13.356%   $187.8422   $187.84   $187.85   $187.80  
  Purchase #6 $117.25   6.678%   $125.08   $125.08   $125.10   $125.10  
  Purchase #7 $247.42   12.121%   $277.4098   $277.41   $277.40   $277.40  
  7 purchase totals = $1,273.35       $1,417.1120   $1,417.11   $1,417.15   $1,417.20