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 $60.43   11.708%   $67.5051   $67.51   $67.50   $67.50  
  Purchase #2 $80.89   8.176%   $87.5036   $87.50   $87.50   $87.50  
  Purchase #3 $113.57   4.603%   $118.7976   $118.80   $118.80   $118.80  
  Purchase #4 $193.97   5.668%   $204.9642   $204.96   $204.95   $205.00  
  Purchase #5 $194.88   5.504%   $205.6062   $205.61   $205.60   $205.60  
  Purchase #6 $237.39   13.672%   $269.846   $269.85   $269.85   $269.80  
  Purchase #7 $206.68   11.152%   $229.729   $229.73   $229.75   $229.70  
  7 purchase totals = $1,087.81       $1,183.9517   $1,183.96   $1,183.95   $1,183.90