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 $128.63   13.654%   $146.1931   $146.19   $146.20   $146.20  
  Purchase #2 $105.66   11.307%   $117.607   $117.61   $117.60   $117.60  
  Purchase #3 $204.47   12.298%   $229.6157   $229.62   $229.60   $229.60  
  Purchase #4 $13.55   8.122%   $14.6505   $14.65   $14.65   $14.70  
  Purchase #5 $91.62   8.291%   $99.2162   $99.22   $99.20   $99.20  
  Purchase #6 $230.48   11.871%   $257.8403   $257.84   $257.85   $257.80  
  Purchase #7 $159.36   6.394%   $169.5495   $169.55   $169.55   $169.50  
  7 purchase totals = $933.77       $1,034.6723   $1,034.68   $1,034.65   $1,034.60