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 $208.33   5.869%   $220.5569   $220.56   $220.55   $220.60  
  Purchase #2 $130.86   6.715%   $139.6472   $139.65   $139.65   $139.60  
  Purchase #3 $23.29   10.855%   $25.8181   $25.82   $25.80   $25.80  
  Purchase #4 $223.96   3.532%   $231.8703   $231.87   $231.85   $231.90  
  Purchase #5 $161.45   11.617%   $180.2056   $180.21   $180.20   $180.20  
  Purchase #6 $63.53   4.594%   $66.4486   $66.45   $66.45   $66.40  
  Purchase #7 $106.91   12.815%   $120.6105   $120.61   $120.60   $120.60  
  7 purchase totals = $918.33       $985.1572   $985.17   $985.10   $985.10