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 $56.67   3.695%   $58.764   $58.76   $58.75   $58.80  
  Purchase #2 $188.96   13.407%   $214.2939   $214.29   $214.30   $214.30  
  Purchase #3 $228.79   9.695%   $250.9712   $250.97   $250.95   $251.00  
  Purchase #4 $59.98   11.324%   $66.7721   $66.77   $66.75   $66.80  
  Purchase #5 $217.59   9.232%   $237.6779   $237.68   $237.70   $237.70  
  Purchase #6 $233.54   9.557%   $255.8594   $255.86   $255.85   $255.90  
  Purchase #7 $240.80   11.374%   $268.1886   $268.19   $268.20   $268.20  
  7 purchase totals = $1,226.33       $1,352.5271   $1,352.52   $1,352.50   $1,352.70