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 $23.72   8.566%   $25.7519   $25.75   $25.75   $25.80  
  Purchase #2 $223.27   6.741%   $238.3206   $238.32   $238.30   $238.30  
  Purchase #3 $174.63   4.226%   $182.0099   $182.01   $182.00   $182.00  
  Purchase #4 $193.64   13.548%   $219.8743   $219.87   $219.85   $219.90  
  Purchase #5 $208.77   7.539%   $224.5092   $224.51   $224.50   $224.50  
  Purchase #6 $59.66   4.857%   $62.5577   $62.56   $62.55   $62.60  
  Purchase #7 $80.88   8.790%   $87.9894   $87.99   $88.00   $88.00  
  7 purchase totals = $964.57       $1,041.0130   $1,041.01   $1,040.95   $1,041.10