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 $59.81   8.653%   $64.9854   $64.99   $65.00   $65.00  
  Purchase #2 $11.29   7.546%   $12.1419   $12.14   $12.15   $12.10  
  Purchase #3 $161.26   5.473%   $170.0858   $170.09   $170.10   $170.10  
  Purchase #4 $204.87   13.259%   $232.0337   $232.03   $232.05   $232.00  
  Purchase #5 $102.81   5.410%   $108.372   $108.37   $108.35   $108.40  
  Purchase #6 $164.93   6.602%   $175.8187   $175.82   $175.80   $175.80  
  Purchase #7 $239.80   3.312%   $247.7422   $247.74   $247.75   $247.70  
  7 purchase totals = $944.77       $1,011.1797   $1,011.18   $1,011.20   $1,011.10