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 $215.46   12.758%   $242.9484   $242.95   $242.95   $242.90  
  Purchase #2 $180.37   11.128%   $200.4416   $200.44   $200.45   $200.40  
  Purchase #3 $97.87   9.494%   $107.1618   $107.16   $107.15   $107.20  
  Purchase #4 $216.48   10.164%   $238.483   $238.48   $238.50   $238.50  
  Purchase #5 $184.94   11.720%   $206.615   $206.62   $206.60   $206.60  
  Purchase #6 $58.32   5.502%   $61.5288   $61.53   $61.55   $61.50  
  Purchase #7 $107.92   5.282%   $113.6203   $113.62   $113.60   $113.60  
  7 purchase totals = $1,061.36       $1,170.7989   $1,170.80   $1,170.80   $1,170.70