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 $57.31   6.711%   $61.1561   $61.16   $61.15   $61.20  
  Purchase #2 $194.38   13.453%   $220.5299   $220.53   $220.55   $220.50  
  Purchase #3 $20.73   12.109%   $23.2402   $23.24   $23.25   $23.20  
  Purchase #4 $72.33   7.335%   $77.6354   $77.64   $77.65   $77.60  
  Purchase #5 $50.96   13.196%   $57.6847   $57.68   $57.70   $57.70  
  Purchase #6 $96.49   10.270%   $106.3995   $106.40   $106.40   $106.40  
  Purchase #7 $238.79   6.663%   $254.7006   $254.70   $254.70   $254.70  
  7 purchase totals = $730.99       $801.3464   $801.35   $801.40   $801.30