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 $48.29   9.350%   $52.8051   $52.81   $52.80   $52.80  
  Purchase #2 $158.35   11.107%   $175.9379   $175.94   $175.95   $175.90  
  Purchase #3 $70.49   6.717%   $75.2248   $75.22   $75.20   $75.20  
  Purchase #4 $84.78   10.474%   $93.6599   $93.66   $93.65   $93.70  
  Purchase #5 $27.28   11.523%   $30.4235   $30.42   $30.40   $30.40  
  Purchase #6 $120.59   11.203%   $134.0997   $134.10   $134.10   $134.10  
  Purchase #7 $126.90   10.524%   $140.255   $140.26   $140.25   $140.30  
  7 purchase totals = $636.68       $702.4059   $702.41   $702.35   $702.40