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 $45.77   8.236%   $49.5396   $49.54   $49.55   $49.50  
  Purchase #2 $191.90   9.419%   $209.9751   $209.98   $210.00   $210.00  
  Purchase #3 $250.69   12.489%   $281.9987   $282.00   $282.00   $282.00  
  Purchase #4 $65.67   12.762%   $74.0508   $74.05   $74.05   $74.10  
  Purchase #5 $19.65   13.287%   $22.2609   $22.26   $22.25   $22.30  
  Purchase #6 $161.56   13.848%   $183.9328   $183.93   $183.95   $183.90  
  Purchase #7 $217.69   12.534%   $244.9753   $244.98   $245.00   $245.00  
  7 purchase totals = $952.93       $1,066.7332   $1,066.74   $1,066.80   $1,066.80