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 $67.53   9.289%   $73.8029   $73.80   $73.80   $73.80  
  Purchase #2 $94.79   10.528%   $104.7695   $104.77   $104.75   $104.80  
  Purchase #3 $68.69   7.277%   $73.6886   $73.69   $73.70   $73.70  
  Purchase #4 $107.43   3.863%   $111.58   $111.58   $111.60   $111.60  
  Purchase #5 $204.66   12.543%   $230.3305   $230.33   $230.35   $230.30  
  Purchase #6 $170.58   5.397%   $179.7862   $179.79   $179.80   $179.80  
  Purchase #7 $108.86   11.131%   $120.9772   $120.98   $121.00   $121.00  
  7 purchase totals = $822.54       $894.9349   $894.94   $895.00   $895.00