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 $234.39   3.108%   $241.6748   $241.67   $241.65   $241.70  
  Purchase #2 $244.80   8.195%   $264.8614   $264.86   $264.85   $264.90  
  Purchase #3 $169.93   8.706%   $184.7241   $184.72   $184.70   $184.70  
  Purchase #4 $149.97   5.355%   $158.0009   $158.00   $158.00   $158.00  
  Purchase #5 $156.88   6.169%   $166.5579   $166.56   $166.55   $166.60  
  Purchase #6 $205.37   5.787%   $217.2548   $217.25   $217.25   $217.30  
  Purchase #7 $56.28   8.806%   $61.236   $61.24   $61.25   $61.20  
  7 purchase totals = $1,217.62       $1,294.3099   $1,294.30   $1,294.25   $1,294.40