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 $236.43   13.284%   $267.8374   $267.84   $267.85   $267.80  
  Purchase #2 $37.74   4.439%   $39.4153   $39.42   $39.40   $39.40  
  Purchase #3 $107.51   3.848%   $111.647   $111.65   $111.65   $111.60  
  Purchase #4 $82.66   13.713%   $93.9952   $94.00   $94.00   $94.00  
  Purchase #5 $63.26   11.756%   $70.6968   $70.70   $70.70   $70.70  
  Purchase #6 $43.78   9.538%   $47.9557   $47.96   $47.95   $48.00  
  Purchase #7 $128.47   5.435%   $135.4523   $135.45   $135.45   $135.50  
  7 purchase totals = $699.85       $766.9997   $767.02   $767.00   $767.00