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 $51.27   9.559%   $56.1709   $56.17   $56.15   $56.20  
  Purchase #2 $210.44   11.114%   $233.8283   $233.83   $233.85   $233.80  
  Purchase #3 $139.35   4.301%   $145.3434   $145.34   $145.35   $145.30  
  Purchase #4 $9.51   9.653%   $10.428   $10.43   $10.45   $10.40  
  Purchase #5 $228.46   11.484%   $254.6963   $254.70   $254.70   $254.70  
  Purchase #6 $88.82   3.252%   $91.7084   $91.71   $91.70   $91.70  
  Purchase #7 $90.61   12.743%   $102.1564   $102.16   $102.15   $102.20  
  7 purchase totals = $818.46       $894.3317   $894.34   $894.35   $894.30