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 $59.93   13.353%   $67.9325   $67.93   $67.95   $67.90  
  Purchase #2 $232.76   7.147%   $249.3954   $249.40   $249.40   $249.40  
  Purchase #3 $195.33   4.507%   $204.1335   $204.13   $204.15   $204.10  
  Purchase #4 $26.70   10.616%   $29.5345   $29.53   $29.55   $29.50  
  Purchase #5 $83.27   6.836%   $88.9623   $88.96   $88.95   $89.00  
  Purchase #6 $116.86   11.614%   $130.4321   $130.43   $130.45   $130.40  
  Purchase #7 $223.35   9.419%   $244.3873   $244.39   $244.40   $244.40  
  7 purchase totals = $938.20       $1,014.7776   $1,014.77   $1,014.85   $1,014.70