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 $141.82   6.122%   $150.5022   $150.50   $150.50   $150.50  
  Purchase #2 $58.26   11.572%   $65.0018   $65.00   $65.00   $65.00  
  Purchase #3 $109.94   9.120%   $119.9665   $119.97   $119.95   $120.00  
  Purchase #4 $206.66   12.841%   $233.1972   $233.20   $233.20   $233.20  
  Purchase #5 $159.51   9.301%   $174.346   $174.35   $174.35   $174.30  
  Purchase #6 $149.77   3.620%   $155.1917   $155.19   $155.20   $155.20  
  Purchase #7 $34.39   3.706%   $35.6645   $35.66   $35.65   $35.70  
  7 purchase totals = $860.35       $933.8699   $933.87   $933.85   $933.90