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 $61.47   3.787%   $63.7979   $63.80   $63.80   $63.80  
  Purchase #2 $238.85   5.641%   $252.3235   $252.32   $252.30   $252.30  
  Purchase #3 $183.93   6.180%   $195.2969   $195.30   $195.30   $195.30  
  Purchase #4 $117.44   6.394%   $124.9491   $124.95   $124.95   $124.90  
  Purchase #5 $205.50   7.223%   $220.3433   $220.34   $220.35   $220.30  
  Purchase #6 $20.63   4.294%   $21.5159   $21.52   $21.50   $21.50  
  Purchase #7 $71.53   4.818%   $74.9763   $74.98   $75.00   $75.00  
  7 purchase totals = $899.35       $953.2029   $953.21   $953.20   $953.10