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 $63.98   7.611%   $68.8495   $68.85   $68.85   $68.80  
  Purchase #2 $103.95   8.203%   $112.477   $112.48   $112.50   $112.50  
  Purchase #3 $225.50   7.524%   $242.4666   $242.47   $242.45   $242.50  
  Purchase #4 $212.79   4.111%   $221.5378   $221.54   $221.55   $221.50  
  Purchase #5 $55.64   12.651%   $62.679   $62.68   $62.70   $62.70  
  Purchase #6 $241.28   8.819%   $262.5585   $262.56   $262.55   $262.60  
  Purchase #7 $128.65   11.826%   $143.8641   $143.86   $143.85   $143.90  
  7 purchase totals = $1,031.79       $1,114.4325   $1,114.44   $1,114.45   $1,114.50