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 $234.77   13.772%   $267.1025   $267.10   $267.10   $267.10  
  Purchase #2 $188.39   13.836%   $214.4556   $214.46   $214.45   $214.50  
  Purchase #3 $87.31   6.292%   $92.8035   $92.80   $92.80   $92.80  
  Purchase #4 $184.42   12.124%   $206.7791   $206.78   $206.80   $206.80  
  Purchase #5 $205.29   6.567%   $218.7714   $218.77   $218.75   $218.80  
  Purchase #6 $225.29   4.679%   $235.8313   $235.83   $235.85   $235.80  
  Purchase #7 $59.81   4.780%   $62.6689   $62.67   $62.65   $62.70  
  7 purchase totals = $1,185.28       $1,298.4123   $1,298.41   $1,298.40   $1,298.50