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 $206.80   9.610%   $226.6735   $226.67   $226.65   $226.70  
  Purchase #2 $72.68   12.819%   $81.9968   $82.00   $82.00   $82.00  
  Purchase #3 $44.45   9.474%   $48.6612   $48.66   $48.65   $48.70  
  Purchase #4 $37.37   11.215%   $41.561   $41.56   $41.55   $41.60  
  Purchase #5 $181.56   9.485%   $198.781   $198.78   $198.80   $198.80  
  Purchase #6 $63.39   4.253%   $66.086   $66.09   $66.10   $66.10  
  Purchase #7 $35.77   8.214%   $38.7081   $38.71   $38.70   $38.70  
  7 purchase totals = $642.02       $702.4676   $702.47   $702.45   $702.60