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 $232.56   12.587%   $261.8323   $261.83   $261.85   $261.80  
  Purchase #2 $134.43   8.869%   $146.3526   $146.35   $146.35   $146.40  
  Purchase #3 $58.91   13.283%   $66.735   $66.74   $66.75   $66.70  
  Purchase #4 $228.88   6.749%   $244.3271   $244.33   $244.35   $244.30  
  Purchase #5 $164.41   5.690%   $173.7649   $173.76   $173.75   $173.80  
  Purchase #6 $94.31   5.593%   $99.5848   $99.58   $99.60   $99.60  
  Purchase #7 $47.25   12.452%   $53.1336   $53.13   $53.15   $53.10  
  7 purchase totals = $960.75       $1,045.7303   $1,045.72   $1,045.80   $1,045.70