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 $210.79   12.340%   $236.8015   $236.80   $236.80   $236.80  
  Purchase #2 $227.75   10.278%   $251.1581   $251.16   $251.15   $251.20  
  Purchase #3 $136.91   13.140%   $154.9   $154.90   $154.90   $154.90  
  Purchase #4 $60.98   10.110%   $67.1451   $67.15   $67.15   $67.10  
  Purchase #5 $31.56   10.508%   $34.8763   $34.88   $34.90   $34.90  
  Purchase #6 $24.41   7.243%   $26.178   $26.18   $26.20   $26.20  
  Purchase #7 $224.46   11.170%   $249.5322   $249.53   $249.55   $249.50  
  7 purchase totals = $916.86       $1,020.5912   $1,020.60   $1,020.65   $1,020.60