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 $85.51   11.495%   $95.3394   $95.34   $95.35   $95.30  
  Purchase #2 $92.93   10.472%   $102.6616   $102.66   $102.65   $102.70  
  Purchase #3 $195.70   4.445%   $204.3989   $204.40   $204.40   $204.40  
  Purchase #4 $196.59   9.289%   $214.8512   $214.85   $214.85   $214.90  
  Purchase #5 $81.29   13.412%   $92.1926   $92.19   $92.20   $92.20  
  Purchase #6 $112.35   9.670%   $123.2142   $123.21   $123.20   $123.20  
  Purchase #7 $110.53   5.797%   $116.9374   $116.94   $116.95   $116.90  
  7 purchase totals = $874.90       $949.5953   $949.59   $949.60   $949.60