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 $200.46   11.628%   $223.7695   $223.77   $223.75   $223.80  
  Purchase #2 $210.95   10.265%   $232.604   $232.60   $232.60   $232.60  
  Purchase #3 $40.55   8.258%   $43.8986   $43.90   $43.90   $43.90  
  Purchase #4 $218.62   7.268%   $234.5093   $234.51   $234.50   $234.50  
  Purchase #5 $236.55   8.528%   $256.723   $256.72   $256.70   $256.70  
  Purchase #6 $135.36   6.861%   $144.647   $144.65   $144.65   $144.60  
  Purchase #7 $93.30   12.564%   $105.0222   $105.02   $105.00   $105.00  
  7 purchase totals = $1,135.79       $1,241.1736   $1,241.17   $1,241.10   $1,241.10