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 $68.45   12.738%   $77.1692   $77.17   $77.15   $77.20  
  Purchase #2 $218.46   9.461%   $239.1285   $239.13   $239.15   $239.10  
  Purchase #3 $74.35   13.147%   $84.1248   $84.12   $84.10   $84.10  
  Purchase #4 $62.29   13.284%   $70.5646   $70.56   $70.55   $70.60  
  Purchase #5 $127.35   6.629%   $135.792   $135.79   $135.80   $135.80  
  Purchase #6 $9.46   7.375%   $10.1577   $10.16   $10.15   $10.20  
  Purchase #7 $126.28   7.133%   $135.2876   $135.29   $135.30   $135.30  
  7 purchase totals = $686.64       $752.2244   $752.22   $752.20   $752.30