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 $92.78   11.647%   $103.5861   $103.59   $103.60   $103.60  
  Purchase #2 $221.84   10.809%   $245.8187   $245.82   $245.80   $245.80  
  Purchase #3 $131.32   6.780%   $140.2235   $140.22   $140.20   $140.20  
  Purchase #4 $179.73   7.580%   $193.3535   $193.35   $193.35   $193.40  
  Purchase #5 $163.96   9.387%   $179.3509   $179.35   $179.35   $179.40  
  Purchase #6 $229.52   13.159%   $259.7225   $259.72   $259.70   $259.70  
  Purchase #7 $141.97   3.205%   $146.5201   $146.52   $146.50   $146.50  
  7 purchase totals = $1,161.12       $1,268.5753   $1,268.57   $1,268.50   $1,268.60