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 $32.53   11.239%   $36.186   $36.19   $36.20   $36.20  
  Purchase #2 $172.95   12.674%   $194.8697   $194.87   $194.85   $194.90  
  Purchase #3 $227.27   12.778%   $256.3106   $256.31   $256.30   $256.30  
  Purchase #4 $233.52   3.119%   $240.8035   $240.80   $240.80   $240.80  
  Purchase #5 $141.38   8.455%   $153.3337   $153.33   $153.35   $153.30  
  Purchase #6 $204.86   8.809%   $222.9061   $222.91   $222.90   $222.90  
  Purchase #7 $54.46   11.697%   $60.8302   $60.83   $60.85   $60.80  
  7 purchase totals = $1,066.97       $1,165.2398   $1,165.24   $1,165.25   $1,165.20