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 $211.81   10.322%   $233.673   $233.67   $233.65   $233.70  
  Purchase #2 $187.57   8.634%   $203.7648   $203.76   $203.75   $203.80  
  Purchase #3 $58.53   8.330%   $63.4055   $63.41   $63.40   $63.40  
  Purchase #4 $179.79   9.803%   $197.4148   $197.41   $197.40   $197.40  
  Purchase #5 $77.88   6.775%   $83.1564   $83.16   $83.15   $83.20  
  Purchase #6 $156.57   6.417%   $166.6171   $166.62   $166.60   $166.60  
  Purchase #7 $43.46   13.439%   $49.3006   $49.30   $49.30   $49.30  
  7 purchase totals = $915.61       $997.3322   $997.33   $997.25   $997.40