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 $206.36   9.130%   $225.2007   $225.20   $225.20   $225.20  
  Purchase #2 $172.58   12.631%   $194.3786   $194.38   $194.40   $194.40  
  Purchase #3 $231.54   13.582%   $262.9878   $262.99   $263.00   $263.00  
  Purchase #4 $179.53   5.371%   $189.1726   $189.17   $189.15   $189.20  
  Purchase #5 $214.46   4.418%   $223.9348   $223.93   $223.95   $223.90  
  Purchase #6 $113.75   8.421%   $123.3289   $123.33   $123.35   $123.30  
  Purchase #7 $236.28   8.473%   $256.3   $256.30   $256.30   $256.30  
  7 purchase totals = $1,354.50       $1,475.3034   $1,475.30   $1,475.35   $1,475.30