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 $184.37   8.365%   $199.7926   $199.79   $199.80   $199.80  
  Purchase #2 $39.41   9.287%   $43.07   $43.07   $43.05   $43.10  
  Purchase #3 $219.27   5.254%   $230.7904   $230.79   $230.80   $230.80  
  Purchase #4 $189.91   11.265%   $211.3034   $211.30   $211.30   $211.30  
  Purchase #5 $69.68   6.818%   $74.4308   $74.43   $74.45   $74.40  
  Purchase #6 $161.97   4.278%   $168.8991   $168.90   $168.90   $168.90  
  Purchase #7 $19.87   9.137%   $21.6855   $21.69   $21.70   $21.70  
  7 purchase totals = $884.48       $949.9718   $949.97   $950.00   $950.00