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 $71.71   5.489%   $75.6462   $75.65   $75.65   $75.60  
  Purchase #2 $55.63   3.358%   $57.4981   $57.50   $57.50   $57.50  
  Purchase #3 $184.78   3.707%   $191.6298   $191.63   $191.65   $191.60  
  Purchase #4 $62.76   4.427%   $65.5384   $65.54   $65.55   $65.50  
  Purchase #5 $228.94   5.564%   $241.6782   $241.68   $241.70   $241.70  
  Purchase #6 $129.38   6.808%   $138.1882   $138.19   $138.20   $138.20  
  Purchase #7 $211.63   5.825%   $223.9574   $223.96   $223.95   $224.00  
  7 purchase totals = $944.83       $994.1363   $994.15   $994.20   $994.10