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 $96.53   5.568%   $101.9048   $101.90   $101.90   $101.90  
  Purchase #2 $202.79   10.133%   $223.3387   $223.34   $223.35   $223.30  
  Purchase #3 $123.74   7.238%   $132.6963   $132.70   $132.70   $132.70  
  Purchase #4 $230.79   12.730%   $260.1696   $260.17   $260.15   $260.20  
  Purchase #5 $45.61   4.837%   $47.8162   $47.82   $47.80   $47.80  
  Purchase #6 $100.87   5.240%   $106.1556   $106.16   $106.15   $106.20  
  Purchase #7 $20.26   3.855%   $21.041   $21.04   $21.05   $21.00  
  7 purchase totals = $820.59       $893.1222   $893.13   $893.10   $893.10