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 $172.30   4.594%   $180.2155   $180.22   $180.20   $180.20  
  Purchase #2 $37.75   13.382%   $42.8017   $42.80   $42.80   $42.80  
  Purchase #3 $186.55   12.796%   $210.4209   $210.42   $210.40   $210.40  
  Purchase #4 $202.28   13.260%   $229.1023   $229.10   $229.10   $229.10  
  Purchase #5 $65.49   7.156%   $70.1765   $70.18   $70.20   $70.20  
  Purchase #6 $95.47   10.678%   $105.6643   $105.66   $105.65   $105.70  
  Purchase #7 $78.72   5.428%   $82.9929   $82.99   $83.00   $83.00  
  7 purchase totals = $838.56       $921.3741   $921.37   $921.35   $921.40