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 $186.67   7.829%   $201.2844   $201.28   $201.30   $201.30  
  Purchase #2 $152.54   8.331%   $165.2481   $165.25   $165.25   $165.20  
  Purchase #3 $195.78   7.174%   $209.8253   $209.83   $209.85   $209.80  
  Purchase #4 $48.98   11.654%   $54.6881   $54.69   $54.70   $54.70  
  Purchase #5 $192.73   13.406%   $218.5674   $218.57   $218.55   $218.60  
  Purchase #6 $164.48   3.846%   $170.8059   $170.81   $170.80   $170.80  
  Purchase #7 $159.90   12.617%   $180.0746   $180.07   $180.05   $180.10  
  7 purchase totals = $1,101.08       $1,200.4938   $1,200.50   $1,200.50   $1,200.50