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 $108.99   11.702%   $121.744   $121.74   $121.75   $121.70  
  Purchase #2 $148.32   4.654%   $155.2228   $155.22   $155.20   $155.20  
  Purchase #3 $52.73   9.244%   $57.6044   $57.60   $57.60   $57.60  
  Purchase #4 $184.54   9.839%   $202.6969   $202.70   $202.70   $202.70  
  Purchase #5 $88.97   5.655%   $94.0013   $94.00   $94.00   $94.00  
  Purchase #6 $15.36   10.483%   $16.9702   $16.97   $16.95   $17.00  
  Purchase #7 $158.84   11.705%   $177.4322   $177.43   $177.45   $177.40  
  7 purchase totals = $757.75       $825.6718   $825.66   $825.65   $825.60