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 $100.90   4.397%   $105.3366   $105.34   $105.35   $105.30  
  Purchase #2 $135.26   4.230%   $140.9815   $140.98   $141.00   $141.00  
  Purchase #3 $20.90   6.205%   $22.1968   $22.20   $22.20   $22.20  
  Purchase #4 $228.35   8.465%   $247.6798   $247.68   $247.70   $247.70  
  Purchase #5 $156.68   12.781%   $176.7053   $176.71   $176.70   $176.70  
  Purchase #6 $205.88   12.607%   $231.8353   $231.84   $231.85   $231.80  
  Purchase #7 $178.46   9.507%   $195.4262   $195.43   $195.45   $195.40  
  7 purchase totals = $1,026.43       $1,120.1615   $1,120.18   $1,120.25   $1,120.10