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 $169.37   13.129%   $191.6066   $191.61   $191.60   $191.60  
  Purchase #2 $67.77   11.845%   $75.7974   $75.80   $75.80   $75.80  
  Purchase #3 $144.58   9.503%   $158.3194   $158.32   $158.30   $158.30  
  Purchase #4 $123.48   8.475%   $133.9449   $133.94   $133.95   $133.90  
  Purchase #5 $240.88   5.433%   $253.967   $253.97   $253.95   $254.00  
  Purchase #6 $24.95   8.275%   $27.0146   $27.01   $27.00   $27.00  
  Purchase #7 $152.94   11.698%   $170.8309   $170.83   $170.85   $170.80  
  7 purchase totals = $923.97       $1,011.4808   $1,011.48   $1,011.45   $1,011.40