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 $249.46   6.606%   $265.9393   $265.94   $265.95   $265.90  
  Purchase #2 $48.77   11.414%   $54.3366   $54.34   $54.35   $54.30  
  Purchase #3 $16.73   4.189%   $17.4308   $17.43   $17.45   $17.40  
  Purchase #4 $166.86   5.314%   $175.7269   $175.73   $175.75   $175.70  
  Purchase #5 $127.45   4.216%   $132.8233   $132.82   $132.80   $132.80  
  Purchase #6 $215.93   7.395%   $231.898   $231.90   $231.90   $231.90  
  Purchase #7 $206.57   6.711%   $220.4329   $220.43   $220.45   $220.40  
  7 purchase totals = $1,031.77       $1,098.5878   $1,098.59   $1,098.65   $1,098.40