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 $231.38   10.790%   $256.3459   $256.35   $256.35   $256.30  
  Purchase #2 $23.37   3.218%   $24.122   $24.12   $24.10   $24.10  
  Purchase #3 $182.91   10.381%   $201.8979   $201.90   $201.90   $201.90  
  Purchase #4 $76.49   11.743%   $85.4722   $85.47   $85.45   $85.50  
  Purchase #5 $169.85   6.372%   $180.6728   $180.67   $180.65   $180.70  
  Purchase #6 $114.36   10.718%   $126.6171   $126.62   $126.60   $126.60  
  Purchase #7 $45.52   12.684%   $51.2938   $51.29   $51.30   $51.30  
  7 purchase totals = $843.88       $926.4217   $926.42   $926.35   $926.40