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 $168.81   3.191%   $174.1967   $174.20   $174.20   $174.20  
  Purchase #2 $103.41   12.473%   $116.3083   $116.31   $116.30   $116.30  
  Purchase #3 $122.92   6.536%   $130.9541   $130.95   $130.95   $131.00  
  Purchase #4 $198.71   6.782%   $212.1865   $212.19   $212.20   $212.20  
  Purchase #5 $152.74   6.681%   $162.9446   $162.94   $162.95   $162.90  
  Purchase #6 $250.54   6.378%   $266.5194   $266.52   $266.50   $266.50  
  Purchase #7 $131.77   7.427%   $141.5566   $141.56   $141.55   $141.60  
  7 purchase totals = $1,128.90       $1,204.6662   $1,204.67   $1,204.65   $1,204.70