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 $226.34   4.838%   $237.2903   $237.29   $237.30   $237.30  
  Purchase #2 $191.26   13.309%   $216.7148   $216.71   $216.70   $216.70  
  Purchase #3 $54.30   13.507%   $61.6343   $61.63   $61.65   $61.60  
  Purchase #4 $244.98   11.255%   $272.5525   $272.55   $272.55   $272.60  
  Purchase #5 $120.74   8.135%   $130.5622   $130.56   $130.55   $130.60  
  Purchase #6 $170.93   3.846%   $177.504   $177.50   $177.50   $177.50  
  Purchase #7 $49.31   7.281%   $52.9003   $52.90   $52.90   $52.90  
  7 purchase totals = $1,057.86       $1,149.1584   $1,149.14   $1,149.15   $1,149.20