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 $184.69   4.660%   $193.2966   $193.30   $193.30   $193.30  
  Purchase #2 $247.26   10.639%   $273.566   $273.57   $273.55   $273.60  
  Purchase #3 $53.70   11.156%   $59.6908   $59.69   $59.70   $59.70  
  Purchase #4 $84.89   5.821%   $89.8314   $89.83   $89.85   $89.80  
  Purchase #5 $183.57   8.802%   $199.7278   $199.73   $199.75   $199.70  
  Purchase #6 $155.85   9.226%   $170.2287   $170.23   $170.25   $170.20  
  Purchase #7 $48.75   4.232%   $50.8131   $50.81   $50.80   $50.80  
  7 purchase totals = $958.71       $1,037.1544   $1,037.16   $1,037.20   $1,037.10