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 $59.63   3.109%   $61.4839   $61.48   $61.50   $61.50  
  Purchase #2 $139.30   3.339%   $143.9512   $143.95   $143.95   $144.00  
  Purchase #3 $117.88   3.115%   $121.552   $121.55   $121.55   $121.60  
  Purchase #4 $132.47   13.409%   $150.2329   $150.23   $150.25   $150.20  
  Purchase #5 $60.93   6.441%   $64.8545   $64.85   $64.85   $64.90  
  Purchase #6 $31.40   10.467%   $34.6866   $34.69   $34.70   $34.70  
  Purchase #7 $160.99   8.163%   $174.1316   $174.13   $174.15   $174.10  
  7 purchase totals = $702.60       $750.8927   $750.88   $750.95   $751.00