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 $226.76   5.243%   $238.649   $238.65   $238.65   $238.60  
  Purchase #2 $104.88   13.535%   $119.0755   $119.08   $119.10   $119.10  
  Purchase #3 $84.62   4.673%   $88.5743   $88.57   $88.55   $88.60  
  Purchase #4 $56.49   4.349%   $58.9468   $58.95   $58.95   $58.90  
  Purchase #5 $120.50   12.422%   $135.4685   $135.47   $135.45   $135.50  
  Purchase #6 $192.96   6.709%   $205.9057   $205.91   $205.90   $205.90  
  Purchase #7 $211.36   7.855%   $227.9623   $227.96   $227.95   $228.00  
  7 purchase totals = $997.57       $1,074.5821   $1,074.59   $1,074.55   $1,074.60