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 $200.98   9.133%   $219.3355   $219.34   $219.35   $219.30  
  Purchase #2 $10.76   3.461%   $11.1324   $11.13   $11.15   $11.10  
  Purchase #3 $50.99   11.522%   $56.8651   $56.87   $56.85   $56.90  
  Purchase #4 $101.37   5.499%   $106.9443   $106.94   $106.95   $106.90  
  Purchase #5 $235.94   10.496%   $260.7043   $260.70   $260.70   $260.70  
  Purchase #6 $154.43   11.729%   $172.5431   $172.54   $172.55   $172.50  
  Purchase #7 $85.44   6.837%   $91.2815   $91.28   $91.30   $91.30  
  7 purchase totals = $839.91       $918.8062   $918.80   $918.85   $918.70