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 $237.48   10.738%   $262.9806   $262.98   $263.00   $263.00  
  Purchase #2 $191.94   7.712%   $206.7424   $206.74   $206.75   $206.70  
  Purchase #3 $171.55   4.556%   $179.3658   $179.37   $179.35   $179.40  
  Purchase #4 $26.84   12.862%   $30.2922   $30.29   $30.30   $30.30  
  Purchase #5 $139.92   8.472%   $151.774   $151.77   $151.75   $151.80  
  Purchase #6 $129.48   12.133%   $145.1898   $145.19   $145.20   $145.20  
  Purchase #7 $68.66   6.811%   $73.3364   $73.34   $73.35   $73.30  
  7 purchase totals = $965.87       $1,049.6812   $1,049.68   $1,049.70   $1,049.70