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 $236.41   13.159%   $267.5192   $267.52   $267.50   $267.50  
  Purchase #2 $49.40   6.458%   $52.5903   $52.59   $52.60   $52.60  
  Purchase #3 $93.85   6.260%   $99.725   $99.73   $99.75   $99.70  
  Purchase #4 $87.66   4.140%   $91.2891   $91.29   $91.30   $91.30  
  Purchase #5 $180.41   13.507%   $204.778   $204.78   $204.80   $204.80  
  Purchase #6 $181.78   13.420%   $206.1749   $206.17   $206.15   $206.20  
  Purchase #7 $41.72   11.841%   $46.6601   $46.66   $46.65   $46.70  
  7 purchase totals = $871.23       $968.7366   $968.74   $968.75   $968.80