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 $164.59   13.213%   $186.3373   $186.34   $186.35   $186.30  
  Purchase #2 $99.39   9.252%   $108.5856   $108.59   $108.60   $108.60  
  Purchase #3 $25.40   3.842%   $26.3759   $26.38   $26.40   $26.40  
  Purchase #4 $201.40   11.618%   $224.7987   $224.80   $224.80   $224.80  
  Purchase #5 $52.70   3.243%   $54.4091   $54.41   $54.40   $54.40  
  Purchase #6 $219.91   3.649%   $227.9345   $227.93   $227.95   $227.90  
  Purchase #7 $195.79   4.306%   $204.2207   $204.22   $204.20   $204.20  
  7 purchase totals = $959.18       $1,032.6618   $1,032.67   $1,032.70   $1,032.60