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 $171.75   7.393%   $184.4475   $184.45   $184.45   $184.40  
  Purchase #2 $72.95   5.607%   $77.0403   $77.04   $77.05   $77.00  
  Purchase #3 $232.48   8.730%   $252.7755   $252.78   $252.80   $252.80  
  Purchase #4 $54.50   3.666%   $56.498   $56.50   $56.50   $56.50  
  Purchase #5 $31.38   6.766%   $33.5032   $33.50   $33.50   $33.50  
  Purchase #6 $88.53   6.119%   $93.9472   $93.95   $93.95   $93.90  
  Purchase #7 $181.46   8.639%   $197.1363   $197.14   $197.15   $197.10  
  7 purchase totals = $833.05       $895.3480   $895.36   $895.40   $895.20