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 $24.76   8.198%   $26.7898   $26.79   $26.80   $26.80  
  Purchase #2 $153.56   11.519%   $171.2486   $171.25   $171.25   $171.20  
  Purchase #3 $143.46   12.173%   $160.9234   $160.92   $160.90   $160.90  
  Purchase #4 $85.96   6.179%   $91.2715   $91.27   $91.25   $91.30  
  Purchase #5 $235.95   8.680%   $256.4305   $256.43   $256.45   $256.40  
  Purchase #6 $217.66   3.421%   $225.1061   $225.11   $225.10   $225.10  
  Purchase #7 $205.61   8.460%   $223.0046   $223.00   $223.00   $223.00  
  7 purchase totals = $1,066.96       $1,154.7745   $1,154.77   $1,154.75   $1,154.70