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 $224.76   7.546%   $241.7204   $241.72   $241.70   $241.70  
  Purchase #2 $62.32   5.751%   $65.904   $65.90   $65.90   $65.90  
  Purchase #3 $48.40   6.111%   $51.3577   $51.36   $51.35   $51.40  
  Purchase #4 $5.78   4.644%   $6.0484   $6.05   $6.05   $6.00  
  Purchase #5 $205.61   12.187%   $230.6677   $230.67   $230.65   $230.70  
  Purchase #6 $57.31   3.250%   $59.1726   $59.17   $59.15   $59.20  
  Purchase #7 $195.87   7.688%   $210.9285   $210.93   $210.95   $210.90  
  7 purchase totals = $800.05       $865.7993   $865.80   $865.75   $865.80