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 $182.57   10.133%   $201.0698   $201.07   $201.05   $201.10  
  Purchase #2 $178.63   13.107%   $202.043   $202.04   $202.05   $202.00  
  Purchase #3 $201.25   7.703%   $216.7523   $216.75   $216.75   $216.80  
  Purchase #4 $199.83   11.669%   $223.1482   $223.15   $223.15   $223.10  
  Purchase #5 $208.55   10.302%   $230.0348   $230.03   $230.05   $230.00  
  Purchase #6 $171.90   5.662%   $181.633   $181.63   $181.65   $181.60  
  Purchase #7 $46.28   5.799%   $48.9638   $48.96   $48.95   $49.00  
  7 purchase totals = $1,189.01       $1,303.6449   $1,303.63   $1,303.65   $1,303.60