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 $247.58   8.540%   $268.7233   $268.72   $268.70   $268.70  
  Purchase #2 $56.71   8.637%   $61.608   $61.61   $61.60   $61.60  
  Purchase #3 $135.51   4.485%   $141.5876   $141.59   $141.60   $141.60  
  Purchase #4 $33.81   7.503%   $36.3468   $36.35   $36.35   $36.30  
  Purchase #5 $234.91   8.431%   $254.7153   $254.72   $254.70   $254.70  
  Purchase #6 $246.64   6.561%   $262.8221   $262.82   $262.80   $262.80  
  Purchase #7 $41.35   11.340%   $46.0391   $46.04   $46.05   $46.00  
  7 purchase totals = $996.51       $1,071.8422   $1,071.85   $1,071.80   $1,071.70