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 $67.60   4.438%   $70.6001   $70.60   $70.60   $70.60  
  Purchase #2 $191.25   6.408%   $203.5053   $203.51   $203.50   $203.50  
  Purchase #3 $88.63   4.406%   $92.535   $92.54   $92.55   $92.50  
  Purchase #4 $206.77   6.710%   $220.6443   $220.64   $220.65   $220.60  
  Purchase #5 $50.42   9.626%   $55.2734   $55.27   $55.25   $55.30  
  Purchase #6 $59.48   8.701%   $64.6554   $64.66   $64.65   $64.70  
  Purchase #7 $80.88   9.779%   $88.7893   $88.79   $88.80   $88.80  
  7 purchase totals = $745.03       $796.0028   $796.01   $796.00   $796.00