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 $155.86   5.755%   $164.8297   $164.83   $164.85   $164.80  
  Purchase #2 $213.83   13.803%   $243.345   $243.35   $243.35   $243.30  
  Purchase #3 $71.43   7.298%   $76.643   $76.64   $76.65   $76.60  
  Purchase #4 $225.55   8.270%   $244.203   $244.20   $244.20   $244.20  
  Purchase #5 $91.46   13.853%   $104.13   $104.13   $104.15   $104.10  
  Purchase #6 $214.69   6.870%   $229.4392   $229.44   $229.45   $229.40  
  Purchase #7 $115.30   13.643%   $131.0304   $131.03   $131.05   $131.00  
  7 purchase totals = $1,088.12       $1,193.6203   $1,193.62   $1,193.70   $1,193.40