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 $82.59   10.574%   $91.3231   $91.32   $91.30   $91.30  
  Purchase #2 $176.59   6.854%   $188.6935   $188.69   $188.70   $188.70  
  Purchase #3 $141.63   8.274%   $153.3485   $153.35   $153.35   $153.30  
  Purchase #4 $234.69   7.502%   $252.2964   $252.30   $252.30   $252.30  
  Purchase #5 $116.90   9.363%   $127.8453   $127.85   $127.85   $127.80  
  Purchase #6 $137.73   8.278%   $149.1313   $149.13   $149.15   $149.10  
  Purchase #7 $101.95   8.511%   $110.627   $110.63   $110.65   $110.60  
  7 purchase totals = $992.08       $1,073.2651   $1,073.27   $1,073.30   $1,073.10