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 $84.97   10.113%   $93.563   $93.56   $93.55   $93.60  
  Purchase #2 $18.84   10.149%   $20.7521   $20.75   $20.75   $20.80  
  Purchase #3 $55.69   6.297%   $59.1968   $59.20   $59.20   $59.20  
  Purchase #4 $61.40   3.128%   $63.3206   $63.32   $63.30   $63.30  
  Purchase #5 $188.90   6.103%   $200.4286   $200.43   $200.45   $200.40  
  Purchase #6 $135.91   8.179%   $147.0261   $147.03   $147.05   $147.00  
  Purchase #7 $28.74   13.608%   $32.6509   $32.65   $32.65   $32.70  
  7 purchase totals = $574.45       $616.9381   $616.94   $616.95   $617.00