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 $53.39   6.698%   $56.9661   $56.97   $56.95   $57.00  
  Purchase #2 $106.81   11.235%   $118.8101   $118.81   $118.80   $118.80  
  Purchase #3 $24.55   13.285%   $27.8115   $27.81   $27.80   $27.80  
  Purchase #4 $95.57   5.847%   $101.158   $101.16   $101.15   $101.20  
  Purchase #5 $116.79   9.375%   $127.7391   $127.74   $127.75   $127.70  
  Purchase #6 $212.93   6.257%   $226.253   $226.25   $226.25   $226.30  
  Purchase #7 $184.74   10.667%   $204.4462   $204.45   $204.45   $204.40  
  7 purchase totals = $794.78       $863.1840   $863.19   $863.15   $863.20