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 $54.39   11.403%   $60.5921   $60.59   $60.60   $60.60  
  Purchase #2 $75.82   7.593%   $81.577   $81.58   $81.60   $81.60  
  Purchase #3 $174.80   12.245%   $196.2043   $196.20   $196.20   $196.20  
  Purchase #4 $234.63   9.336%   $256.5351   $256.54   $256.55   $256.50  
  Purchase #5 $211.57   10.503%   $233.7912   $233.79   $233.80   $233.80  
  Purchase #6 $110.34   6.404%   $117.4062   $117.41   $117.40   $117.40  
  Purchase #7 $17.53   7.337%   $18.8162   $18.82   $18.80   $18.80  
  7 purchase totals = $879.08       $964.9221   $964.93   $964.95   $964.90