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 $200.73   3.541%   $207.8378   $207.84   $207.85   $207.80  
  Purchase #2 $211.37   5.639%   $223.2892   $223.29   $223.30   $223.30  
  Purchase #3 $50.67   4.107%   $52.751   $52.75   $52.75   $52.80  
  Purchase #4 $44.33   9.831%   $48.6881   $48.69   $48.70   $48.70  
  Purchase #5 $47.69   3.226%   $49.2285   $49.23   $49.25   $49.20  
  Purchase #6 $126.87   9.493%   $138.9138   $138.91   $138.90   $138.90  
  Purchase #7 $9.65   6.658%   $10.2925   $10.29   $10.30   $10.30  
  7 purchase totals = $691.31       $731.0009   $731.00   $731.05   $731.00