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 $228.44   8.723%   $248.3668   $248.37   $248.35   $248.40  
  Purchase #2 $119.88   5.780%   $126.8091   $126.81   $126.80   $126.80  
  Purchase #3 $144.53   3.147%   $149.0784   $149.08   $149.10   $149.10  
  Purchase #4 $60.47   6.378%   $64.3268   $64.33   $64.35   $64.30  
  Purchase #5 $92.62   13.361%   $104.995   $105.00   $105.00   $105.00  
  Purchase #6 $125.28   13.818%   $142.5912   $142.59   $142.60   $142.60  
  Purchase #7 $231.68   6.745%   $247.3068   $247.31   $247.30   $247.30  
  7 purchase totals = $1,002.90       $1,083.4741   $1,083.49   $1,083.50   $1,083.50