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 $48.35   11.163%   $53.7473   $53.75   $53.75   $53.70  
  Purchase #2 $229.85   9.146%   $250.8721   $250.87   $250.85   $250.90  
  Purchase #3 $51.52   3.838%   $53.4973   $53.50   $53.50   $53.50  
  Purchase #4 $218.36   11.166%   $242.7421   $242.74   $242.75   $242.70  
  Purchase #5 $111.57   8.487%   $121.0389   $121.04   $121.05   $121.00  
  Purchase #6 $201.34   5.290%   $211.9909   $211.99   $212.00   $212.00  
  Purchase #7 $73.52   7.452%   $78.9987   $79.00   $79.00   $79.00  
  7 purchase totals = $934.51       $1,012.8873   $1,012.89   $1,012.90   $1,012.80