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 $114.85   12.609%   $129.3314   $129.33   $129.35   $129.30  
  Purchase #2 $213.32   8.741%   $231.9663   $231.97   $231.95   $232.00  
  Purchase #3 $151.84   3.399%   $157.001   $157.00   $157.00   $157.00  
  Purchase #4 $227.73   5.732%   $240.7835   $240.78   $240.80   $240.80  
  Purchase #5 $82.91   5.192%   $87.2147   $87.21   $87.20   $87.20  
  Purchase #6 $167.57   7.419%   $180.002   $180.00   $180.00   $180.00  
  Purchase #7 $193.25   11.411%   $215.3018   $215.30   $215.30   $215.30  
  7 purchase totals = $1,151.47       $1,241.6007   $1,241.59   $1,241.60   $1,241.60