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 $122.52   7.572%   $131.7972   $131.80   $131.80   $131.80  
  Purchase #2 $182.65   6.211%   $193.9944   $193.99   $194.00   $194.00  
  Purchase #3 $126.30   4.870%   $132.4508   $132.45   $132.45   $132.50  
  Purchase #4 $150.62   5.159%   $158.3905   $158.39   $158.40   $158.40  
  Purchase #5 $114.36   10.407%   $126.2614   $126.26   $126.25   $126.30  
  Purchase #6 $183.26   10.484%   $202.473   $202.47   $202.45   $202.50  
  Purchase #7 $68.55   12.471%   $77.0989   $77.10   $77.10   $77.10  
  7 purchase totals = $948.26       $1,022.4662   $1,022.46   $1,022.45   $1,022.60