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 $55.37   11.134%   $61.5349   $61.53   $61.55   $61.50  
  Purchase #2 $21.59   7.181%   $23.1404   $23.14   $23.15   $23.10  
  Purchase #3 $66.78   5.165%   $70.2292   $70.23   $70.25   $70.20  
  Purchase #4 $193.44   12.331%   $217.2931   $217.29   $217.30   $217.30  
  Purchase #5 $162.96   13.277%   $184.5962   $184.60   $184.60   $184.60  
  Purchase #6 $121.94   11.751%   $136.2692   $136.27   $136.25   $136.30  
  Purchase #7 $69.97   5.794%   $74.0241   $74.02   $74.00   $74.00  
  7 purchase totals = $692.05       $767.0871   $767.08   $767.10   $767.00