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 $214.32   12.844%   $241.8473   $241.85   $241.85   $241.80  
  Purchase #2 $139.78   11.744%   $156.1958   $156.20   $156.20   $156.20  
  Purchase #3 $202.58   9.220%   $221.2579   $221.26   $221.25   $221.30  
  Purchase #4 $89.78   5.262%   $94.5042   $94.50   $94.50   $94.50  
  Purchase #5 $99.52   9.458%   $108.9326   $108.93   $108.95   $108.90  
  Purchase #6 $241.52   9.140%   $263.5949   $263.59   $263.60   $263.60  
  Purchase #7 $249.80   11.516%   $278.567   $278.57   $278.55   $278.60  
  7 purchase totals = $1,237.30       $1,364.8997   $1,364.90   $1,364.90   $1,364.90