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 $178.60   4.760%   $187.1014   $187.10   $187.10   $187.10  
  Purchase #2 $147.73   3.801%   $153.3452   $153.35   $153.35   $153.30  
  Purchase #3 $71.95   3.327%   $74.3438   $74.34   $74.35   $74.30  
  Purchase #4 $214.54   7.703%   $231.066   $231.07   $231.05   $231.10  
  Purchase #5 $66.93   3.603%   $69.3415   $69.34   $69.35   $69.30  
  Purchase #6 $11.27   9.647%   $12.3572   $12.36   $12.35   $12.40  
  Purchase #7 $203.28   12.346%   $228.3769   $228.38   $228.40   $228.40  
  7 purchase totals = $894.30       $955.9320   $955.94   $955.95   $955.90