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 $55.52   11.177%   $61.7255   $61.73   $61.75   $61.70  
  Purchase #2 $241.78   12.404%   $271.7704   $271.77   $271.75   $271.80  
  Purchase #3 $211.75   5.272%   $222.9135   $222.91   $222.90   $222.90  
  Purchase #4 $37.51   13.601%   $42.6117   $42.61   $42.60   $42.60  
  Purchase #5 $151.66   7.593%   $163.1755   $163.18   $163.20   $163.20  
  Purchase #6 $188.40   9.864%   $206.9838   $206.98   $207.00   $207.00  
  Purchase #7 $109.42   12.424%   $123.0143   $123.01   $123.00   $123.00  
  7 purchase totals = $996.04       $1,092.1947   $1,092.19   $1,092.20   $1,092.20