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 $88.83   5.452%   $93.673   $93.67   $93.65   $93.70  
  Purchase #2 $105.34   4.721%   $110.3131   $110.31   $110.30   $110.30  
  Purchase #3 $63.56   8.244%   $68.7999   $68.80   $68.80   $68.80  
  Purchase #4 $54.85   6.755%   $58.5551   $58.56   $58.55   $58.60  
  Purchase #5 $101.37   9.729%   $111.2323   $111.23   $111.25   $111.20  
  Purchase #6 $171.76   13.740%   $195.3598   $195.36   $195.35   $195.40  
  Purchase #7 $225.36   10.529%   $249.0882   $249.09   $249.10   $249.10  
  7 purchase totals = $811.07       $887.0214   $887.02   $887.00   $887.10