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 $204.52   10.109%   $225.1949   $225.19   $225.20   $225.20  
  Purchase #2 $44.38   6.550%   $47.2869   $47.29   $47.30   $47.30  
  Purchase #3 $151.88   9.102%   $165.7041   $165.70   $165.70   $165.70  
  Purchase #4 $113.47   5.523%   $119.7369   $119.74   $119.75   $119.70  
  Purchase #5 $185.42   9.749%   $203.4966   $203.50   $203.50   $203.50  
  Purchase #6 $31.38   11.145%   $34.8773   $34.88   $34.90   $34.90  
  Purchase #7 $210.79   7.390%   $226.3674   $226.37   $226.35   $226.40  
  7 purchase totals = $941.84       $1,022.6641   $1,022.67   $1,022.70   $1,022.70