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 $74.81   10.336%   $82.5424   $82.54   $82.55   $82.50  
  Purchase #2 $187.66   7.814%   $202.3238   $202.32   $202.30   $202.30  
  Purchase #3 $213.55   6.488%   $227.4051   $227.41   $227.40   $227.40  
  Purchase #4 $142.30   7.751%   $153.3297   $153.33   $153.35   $153.30  
  Purchase #5 $51.62   13.765%   $58.7255   $58.73   $58.75   $58.70  
  Purchase #6 $13.80   13.514%   $15.6649   $15.66   $15.65   $15.70  
  Purchase #7 $243.44   12.647%   $274.2279   $274.23   $274.25   $274.20  
  7 purchase totals = $927.18       $1,014.2193   $1,014.22   $1,014.25   $1,014.10