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 $10.85   3.353%   $11.2138   $11.21   $11.20   $11.20  
  Purchase #2 $178.70   10.825%   $198.0443   $198.04   $198.05   $198.00  
  Purchase #3 $154.42   6.431%   $164.3508   $164.35   $164.35   $164.40  
  Purchase #4 $204.46   6.633%   $218.0218   $218.02   $218.00   $218.00  
  Purchase #5 $42.82   11.260%   $47.6415   $47.64   $47.65   $47.60  
  Purchase #6 $163.38   4.148%   $170.157   $170.16   $170.15   $170.20  
  Purchase #7 $222.35   4.534%   $232.4313   $232.43   $232.45   $232.40  
  7 purchase totals = $976.98       $1,041.8605   $1,041.85   $1,041.85   $1,041.80