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 $61.46   7.259%   $65.9214   $65.92   $65.90   $65.90  
  Purchase #2 $130.35   13.493%   $147.9381   $147.94   $147.95   $147.90  
  Purchase #3 $241.31   6.644%   $257.3426   $257.34   $257.35   $257.30  
  Purchase #4 $211.29   8.739%   $229.7546   $229.75   $229.75   $229.80  
  Purchase #5 $238.85   3.347%   $246.8443   $246.84   $246.85   $246.80  
  Purchase #6 $51.83   11.330%   $57.7023   $57.70   $57.70   $57.70  
  Purchase #7 $49.26   13.373%   $55.8475   $55.85   $55.85   $55.80  
  7 purchase totals = $984.35       $1,061.3508   $1,061.34   $1,061.35   $1,061.20