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 $132.99   10.749%   $147.2851   $147.29   $147.30   $147.30  
  Purchase #2 $81.56   12.707%   $91.9238   $91.92   $91.90   $91.90  
  Purchase #3 $224.49   5.842%   $237.6047   $237.60   $237.60   $237.60  
  Purchase #4 $52.67   10.157%   $58.0197   $58.02   $58.00   $58.00  
  Purchase #5 $122.44   9.709%   $134.3277   $134.33   $134.35   $134.30  
  Purchase #6 $55.61   11.408%   $61.954   $61.95   $61.95   $62.00  
  Purchase #7 $72.76   3.528%   $75.327   $75.33   $75.35   $75.30  
  7 purchase totals = $742.52       $806.4420   $806.44   $806.45   $806.40