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 $69.48   10.619%   $76.8581   $76.86   $76.85   $76.90  
  Purchase #2 $190.54   7.169%   $204.1998   $204.20   $204.20   $204.20  
  Purchase #3 $108.42   8.694%   $117.846   $117.85   $117.85   $117.80  
  Purchase #4 $243.28   6.480%   $259.0445   $259.04   $259.05   $259.00  
  Purchase #5 $39.99   12.300%   $44.9088   $44.91   $44.90   $44.90  
  Purchase #6 $220.56   11.645%   $246.2442   $246.24   $246.25   $246.20  
  Purchase #7 $49.56   12.114%   $55.5637   $55.56   $55.55   $55.60  
  7 purchase totals = $921.83       $1,004.6651   $1,004.66   $1,004.65   $1,004.60