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 $138.96   11.245%   $154.5861   $154.59   $154.60   $154.60  
  Purchase #2 $229.53   11.188%   $255.2098   $255.21   $255.20   $255.20  
  Purchase #3 $59.41   4.417%   $62.0341   $62.03   $62.05   $62.00  
  Purchase #4 $171.67   7.389%   $184.3547   $184.35   $184.35   $184.40  
  Purchase #5 $158.78   3.649%   $164.5739   $164.57   $164.55   $164.60  
  Purchase #6 $53.47   4.679%   $55.9719   $55.97   $55.95   $56.00  
  Purchase #7 $186.35   6.270%   $198.0341   $198.03   $198.05   $198.00  
  7 purchase totals = $998.17       $1,074.7646   $1,074.75   $1,074.75   $1,074.80