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 $14.87   11.486%   $16.578   $16.58   $16.60   $16.60  
  Purchase #2 $160.35   8.669%   $174.2507   $174.25   $174.25   $174.30  
  Purchase #3 $157.39   11.300%   $175.1751   $175.18   $175.20   $175.20  
  Purchase #4 $220.79   9.227%   $241.1623   $241.16   $241.15   $241.20  
  Purchase #5 $34.27   13.741%   $38.979   $38.98   $39.00   $39.00  
  Purchase #6 $192.85   7.566%   $207.441   $207.44   $207.45   $207.40  
  Purchase #7 $54.46   9.492%   $59.6293   $59.63   $59.65   $59.60  
  7 purchase totals = $834.98       $913.2154   $913.22   $913.30   $913.30