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 $203.97   10.397%   $225.1768   $225.18   $225.20   $225.20  
  Purchase #2 $216.78   4.712%   $226.9947   $226.99   $227.00   $227.00  
  Purchase #3 $202.80   10.381%   $223.8527   $223.85   $223.85   $223.90  
  Purchase #4 $227.66   12.406%   $255.9035   $255.90   $255.90   $255.90  
  Purchase #5 $58.65   10.378%   $64.7367   $64.74   $64.75   $64.70  
  Purchase #6 $193.65   13.224%   $219.2583   $219.26   $219.25   $219.30  
  Purchase #7 $6.91   6.845%   $7.383   $7.38   $7.40   $7.40  
  7 purchase totals = $1,110.42       $1,223.3057   $1,223.30   $1,223.35   $1,223.40