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 $119.31   5.802%   $126.2324   $126.23   $126.25   $126.20  
  Purchase #2 $87.34   4.641%   $91.3934   $91.39   $91.40   $91.40  
  Purchase #3 $95.74   6.869%   $102.3164   $102.32   $102.30   $102.30  
  Purchase #4 $219.29   12.846%   $247.46   $247.46   $247.45   $247.50  
  Purchase #5 $53.35   8.118%   $57.681   $57.68   $57.70   $57.70  
  Purchase #6 $11.97   5.437%   $12.6208   $12.62   $12.60   $12.60  
  Purchase #7 $201.67   6.301%   $214.3772   $214.38   $214.40   $214.40  
  7 purchase totals = $788.67       $852.0812   $852.08   $852.10   $852.10