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 $229.57   13.245%   $259.9765   $259.98   $260.00   $260.00  
  Purchase #2 $184.80   6.602%   $197.0005   $197.00   $197.00   $197.00  
  Purchase #3 $224.97   7.174%   $241.1093   $241.11   $241.10   $241.10  
  Purchase #4 $125.75   8.124%   $135.9659   $135.97   $135.95   $136.00  
  Purchase #5 $148.85   11.271%   $165.6269   $165.63   $165.65   $165.60  
  Purchase #6 $202.42   7.868%   $218.3464   $218.35   $218.35   $218.30  
  Purchase #7 $219.91   3.702%   $228.0511   $228.05   $228.05   $228.10  
  7 purchase totals = $1,336.27       $1,446.0766   $1,446.09   $1,446.10   $1,446.10