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 $83.46   10.114%   $91.9011   $91.90   $91.90   $91.90  
  Purchase #2 $104.29   11.645%   $116.4346   $116.43   $116.45   $116.40  
  Purchase #3 $159.43   3.478%   $164.975   $164.98   $165.00   $165.00  
  Purchase #4 $205.95   13.190%   $233.1148   $233.11   $233.10   $233.10  
  Purchase #5 $205.91   7.690%   $221.7445   $221.74   $221.75   $221.70  
  Purchase #6 $192.48   11.567%   $214.7442   $214.74   $214.75   $214.70  
  Purchase #7 $222.51   13.584%   $252.7358   $252.74   $252.75   $252.70  
  7 purchase totals = $1,174.03       $1,295.6500   $1,295.64   $1,295.70   $1,295.50