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 $205.37   13.654%   $233.4112   $233.41   $233.40   $233.40  
  Purchase #2 $228.84   11.736%   $255.6967   $255.70   $255.70   $255.70  
  Purchase #3 $184.64   3.242%   $190.626   $190.63   $190.65   $190.60  
  Purchase #4 $135.82   7.588%   $146.126   $146.13   $146.15   $146.10  
  Purchase #5 $208.94   7.112%   $223.7998   $223.80   $223.80   $223.80  
  Purchase #6 $70.90   7.133%   $75.9573   $75.96   $75.95   $76.00  
  Purchase #7 $172.93   8.223%   $187.15   $187.15   $187.15   $187.20  
  7 purchase totals = $1,207.44       $1,312.7670   $1,312.78   $1,312.80   $1,312.80