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 $214.61   6.794%   $229.1906   $229.19   $229.20   $229.20  
  Purchase #2 $216.33   9.675%   $237.2599   $237.26   $237.25   $237.30  
  Purchase #3 $238.29   11.436%   $265.5408   $265.54   $265.55   $265.50  
  Purchase #4 $102.96   7.761%   $110.9507   $110.95   $110.95   $111.00  
  Purchase #5 $24.91   6.811%   $26.6066   $26.61   $26.60   $26.60  
  Purchase #6 $130.56   7.142%   $139.8846   $139.88   $139.90   $139.90  
  Purchase #7 $62.37   12.457%   $70.1394   $70.14   $70.15   $70.10  
  7 purchase totals = $990.03       $1,079.5726   $1,079.57   $1,079.60   $1,079.60