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 $94.50   13.851%   $107.5892   $107.59   $107.60   $107.60  
  Purchase #2 $36.38   8.298%   $39.3988   $39.40   $39.40   $39.40  
  Purchase #3 $161.61   6.439%   $172.0161   $172.02   $172.00   $172.00  
  Purchase #4 $210.72   11.750%   $235.4796   $235.48   $235.50   $235.50  
  Purchase #5 $75.91   9.285%   $82.9582   $82.96   $82.95   $83.00  
  Purchase #6 $142.30   12.549%   $160.1572   $160.16   $160.15   $160.20  
  Purchase #7 $203.36   11.465%   $226.6752   $226.68   $226.70   $226.70  
  7 purchase totals = $924.78       $1,024.2743   $1,024.29   $1,024.30   $1,024.40