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 $24.43   9.143%   $26.6636   $26.66   $26.65   $26.70  
  Purchase #2 $189.43   13.166%   $214.3704   $214.37   $214.35   $214.40  
  Purchase #3 $110.29   7.755%   $118.843   $118.84   $118.85   $118.80  
  Purchase #4 $91.95   3.221%   $94.9117   $94.91   $94.90   $94.90  
  Purchase #5 $190.61   12.717%   $214.8499   $214.85   $214.85   $214.80  
  Purchase #6 $128.38   6.192%   $136.3293   $136.33   $136.35   $136.30  
  Purchase #7 $88.57   11.219%   $98.5067   $98.51   $98.50   $98.50  
  7 purchase totals = $823.66       $904.4746   $904.47   $904.45   $904.40