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 $108.74   3.721%   $112.7862   $112.79   $112.80   $112.80  
  Purchase #2 $58.55   11.581%   $65.3307   $65.33   $65.35   $65.30  
  Purchase #3 $6.27   12.122%   $7.03   $7.03   $7.05   $7.00  
  Purchase #4 $44.75   12.615%   $50.3952   $50.40   $50.40   $50.40  
  Purchase #5 $225.74   5.472%   $238.0925   $238.09   $238.10   $238.10  
  Purchase #6 $167.78   3.461%   $173.5869   $173.59   $173.60   $173.60  
  Purchase #7 $92.82   3.231%   $95.819   $95.82   $95.80   $95.80  
  7 purchase totals = $704.65       $743.0405   $743.05   $743.10   $743.00