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 $88.98   3.864%   $92.4182   $92.42   $92.40   $92.40  
  Purchase #2 $73.41   8.364%   $79.55   $79.55   $79.55   $79.60  
  Purchase #3 $98.80   6.616%   $105.3366   $105.34   $105.35   $105.30  
  Purchase #4 $61.54   3.310%   $63.577   $63.58   $63.60   $63.60  
  Purchase #5 $43.46   11.691%   $48.5409   $48.54   $48.55   $48.50  
  Purchase #6 $183.84   8.519%   $199.5013   $199.50   $199.50   $199.50  
  Purchase #7 $155.74   11.867%   $174.2217   $174.22   $174.20   $174.20  
  7 purchase totals = $705.77       $763.1457   $763.15   $763.15   $763.10