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 $134.90   7.281%   $144.7221   $144.72   $144.70   $144.70  
  Purchase #2 $245.31   12.267%   $275.4022   $275.40   $275.40   $275.40  
  Purchase #3 $44.67   4.608%   $46.7284   $46.73   $46.75   $46.70  
  Purchase #4 $122.39   9.178%   $133.623   $133.62   $133.60   $133.60  
  Purchase #5 $70.87   6.346%   $75.3674   $75.37   $75.35   $75.40  
  Purchase #6 $54.41   3.284%   $56.1968   $56.20   $56.20   $56.20  
  Purchase #7 $22.96   5.789%   $24.2892   $24.29   $24.30   $24.30  
  7 purchase totals = $695.51       $756.3291   $756.33   $756.30   $756.30