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 $226.29   6.793%   $241.6619   $241.66   $241.65   $241.70  
  Purchase #2 $219.89   12.183%   $246.6792   $246.68   $246.70   $246.70  
  Purchase #3 $109.32   11.749%   $122.164   $122.16   $122.15   $122.20  
  Purchase #4 $96.88   11.624%   $108.1413   $108.14   $108.15   $108.10  
  Purchase #5 $231.98   5.294%   $244.261   $244.26   $244.25   $244.30  
  Purchase #6 $83.66   5.162%   $87.9785   $87.98   $88.00   $88.00  
  Purchase #7 $232.94   12.630%   $262.3603   $262.36   $262.35   $262.40  
  7 purchase totals = $1,200.96       $1,313.2462   $1,313.24   $1,313.25   $1,313.40