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 $191.55   9.784%   $210.2913   $210.29   $210.30   $210.30  
  Purchase #2 $243.69   13.153%   $275.7425   $275.74   $275.75   $275.70  
  Purchase #3 $216.97   13.451%   $246.1546   $246.15   $246.15   $246.20  
  Purchase #4 $104.82   7.433%   $112.6113   $112.61   $112.60   $112.60  
  Purchase #5 $39.56   12.142%   $44.3634   $44.36   $44.35   $44.40  
  Purchase #6 $202.36   4.360%   $211.1829   $211.18   $211.20   $211.20  
  Purchase #7 $129.43   11.524%   $144.3455   $144.35   $144.35   $144.30  
  7 purchase totals = $1,128.38       $1,244.6915   $1,244.68   $1,244.70   $1,244.70