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 $170.50   11.855%   $190.7128   $190.71   $190.70   $190.70  
  Purchase #2 $58.79   10.657%   $65.0553   $65.06   $65.05   $65.10  
  Purchase #3 $31.80   7.135%   $34.0689   $34.07   $34.05   $34.10  
  Purchase #4 $68.38   7.123%   $73.2507   $73.25   $73.25   $73.30  
  Purchase #5 $53.51   5.441%   $56.4215   $56.42   $56.40   $56.40  
  Purchase #6 $92.72   3.581%   $96.0403   $96.04   $96.05   $96.00  
  Purchase #7 $207.56   4.796%   $217.5146   $217.51   $217.50   $217.50  
  7 purchase totals = $683.26       $733.0641   $733.06   $733.00   $733.10