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 $131.38   3.573%   $136.0742   $136.07   $136.05   $136.10  
  Purchase #2 $146.32   7.753%   $157.6642   $157.66   $157.65   $157.70  
  Purchase #3 $212.55   6.103%   $225.5219   $225.52   $225.50   $225.50  
  Purchase #4 $246.53   5.571%   $260.2642   $260.26   $260.25   $260.30  
  Purchase #5 $11.43   9.562%   $12.5229   $12.52   $12.50   $12.50  
  Purchase #6 $93.65   3.245%   $96.6889   $96.69   $96.70   $96.70  
  Purchase #7 $125.86   6.222%   $133.691   $133.69   $133.70   $133.70  
  7 purchase totals = $967.72       $1,022.4273   $1,022.41   $1,022.35   $1,022.50