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 $59.69   13.705%   $67.8705   $67.87   $67.85   $67.90  
  Purchase #2 $118.80   6.655%   $126.7061   $126.71   $126.70   $126.70  
  Purchase #3 $216.58   6.689%   $231.067   $231.07   $231.05   $231.10  
  Purchase #4 $56.86   7.201%   $60.9545   $60.95   $60.95   $61.00  
  Purchase #5 $249.81   3.729%   $259.1254   $259.13   $259.15   $259.10  
  Purchase #6 $170.34   12.424%   $191.503   $191.50   $191.50   $191.50  
  Purchase #7 $82.53   12.740%   $93.0443   $93.04   $93.05   $93.00  
  7 purchase totals = $954.61       $1,030.2708   $1,030.27   $1,030.25   $1,030.30