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 $168.53   9.753%   $184.9667   $184.97   $184.95   $185.00  
  Purchase #2 $132.29   5.402%   $139.4363   $139.44   $139.45   $139.40  
  Purchase #3 $183.26   6.534%   $195.2342   $195.23   $195.25   $195.20  
  Purchase #4 $53.93   9.841%   $59.2373   $59.24   $59.25   $59.20  
  Purchase #5 $86.33   9.773%   $94.767   $94.77   $94.75   $94.80  
  Purchase #6 $106.97   8.646%   $116.2186   $116.22   $116.20   $116.20  
  Purchase #7 $143.89   6.402%   $153.1018   $153.10   $153.10   $153.10  
  7 purchase totals = $875.20       $942.9619   $942.97   $942.95   $942.90