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 $59.53   9.151%   $64.9776   $64.98   $65.00   $65.00  
  Purchase #2 $192.37   9.481%   $210.6086   $210.61   $210.60   $210.60  
  Purchase #3 $20.54   8.655%   $22.3177   $22.32   $22.30   $22.30  
  Purchase #4 $184.29   8.862%   $200.6218   $200.62   $200.60   $200.60  
  Purchase #5 $144.76   10.541%   $160.0192   $160.02   $160.00   $160.00  
  Purchase #6 $190.57   9.775%   $209.1982   $209.20   $209.20   $209.20  
  Purchase #7 $124.44   9.292%   $136.003   $136.00   $136.00   $136.00  
  7 purchase totals = $916.50       $1,003.7461   $1,003.75   $1,003.70   $1,003.70