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 $65.71   8.855%   $71.5286   $71.53   $71.55   $71.50  
  Purchase #2 $211.25   10.283%   $232.9728   $232.97   $232.95   $233.00  
  Purchase #3 $100.80   9.446%   $110.3216   $110.32   $110.30   $110.30  
  Purchase #4 $117.97   10.639%   $130.5208   $130.52   $130.50   $130.50  
  Purchase #5 $199.39   9.174%   $217.682   $217.68   $217.70   $217.70  
  Purchase #6 $183.95   10.751%   $203.7265   $203.73   $203.75   $203.70  
  Purchase #7 $95.93   9.423%   $104.9695   $104.97   $104.95   $105.00  
  7 purchase totals = $975.00       $1,071.7218   $1,071.72   $1,071.70   $1,071.70