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 $205.68   13.265%   $232.9635   $232.96   $232.95   $233.00  
  Purchase #2 $95.65   10.340%   $105.5402   $105.54   $105.55   $105.50  
  Purchase #3 $36.46   9.110%   $39.7815   $39.78   $39.80   $39.80  
  Purchase #4 $226.58   3.117%   $233.6425   $233.64   $233.65   $233.60  
  Purchase #5 $63.69   10.192%   $70.1813   $70.18   $70.20   $70.20  
  Purchase #6 $74.67   6.398%   $79.4474   $79.45   $79.45   $79.40  
  Purchase #7 $208.55   10.700%   $230.8649   $230.86   $230.85   $230.90  
  7 purchase totals = $911.28       $992.4213   $992.41   $992.45   $992.40