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 $217.32   12.144%   $243.7113   $243.71   $243.70   $243.70  
  Purchase #2 $225.57   12.329%   $253.3805   $253.38   $253.40   $253.40  
  Purchase #3 $249.45   13.490%   $283.1008   $283.10   $283.10   $283.10  
  Purchase #4 $91.98   5.538%   $97.0739   $97.07   $97.05   $97.10  
  Purchase #5 $175.67   5.553%   $185.425   $185.43   $185.45   $185.40  
  Purchase #6 $53.76   9.490%   $58.8618   $58.86   $58.85   $58.90  
  Purchase #7 $247.67   8.306%   $268.2415   $268.24   $268.25   $268.20  
  7 purchase totals = $1,261.42       $1,389.7948   $1,389.79   $1,389.80   $1,389.80