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 $56.33   11.368%   $62.7336   $62.73   $62.75   $62.70  
  Purchase #2 $186.26   3.832%   $193.3975   $193.40   $193.40   $193.40  
  Purchase #3 $76.28   3.673%   $79.0818   $79.08   $79.10   $79.10  
  Purchase #4 $150.83   10.248%   $166.2871   $166.29   $166.30   $166.30  
  Purchase #5 $66.26   7.165%   $71.0075   $71.01   $71.00   $71.00  
  Purchase #6 $49.35   8.685%   $53.636   $53.64   $53.65   $53.60  
  Purchase #7 $52.40   9.292%   $57.269   $57.27   $57.25   $57.30  
  7 purchase totals = $637.71       $683.4125   $683.42   $683.45   $683.40