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 $9.90   5.390%   $10.4336   $10.43   $10.45   $10.40  
  Purchase #2 $52.48   7.331%   $56.3273   $56.33   $56.35   $56.30  
  Purchase #3 $111.27   12.433%   $125.1042   $125.10   $125.10   $125.10  
  Purchase #4 $37.68   3.853%   $39.1318   $39.13   $39.15   $39.10  
  Purchase #5 $71.26   11.401%   $79.3844   $79.38   $79.40   $79.40  
  Purchase #6 $88.40   6.109%   $93.8004   $93.80   $93.80   $93.80  
  Purchase #7 $153.86   9.434%   $168.3752   $168.38   $168.40   $168.40  
  7 purchase totals = $524.85       $572.5569   $572.55   $572.65   $572.50