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 $241.82   10.521%   $267.2619   $267.26   $267.25   $267.30  
  Purchase #2 $20.72   6.253%   $22.0156   $22.02   $22.00   $22.00  
  Purchase #3 $177.46   3.317%   $183.3463   $183.35   $183.35   $183.30  
  Purchase #4 $152.88   13.120%   $172.9379   $172.94   $172.95   $172.90  
  Purchase #5 $80.76   3.634%   $83.6948   $83.69   $83.70   $83.70  
  Purchase #6 $102.47   5.373%   $107.9757   $107.98   $108.00   $108.00  
  Purchase #7 $220.25   8.498%   $238.9668   $238.97   $238.95   $239.00  
  7 purchase totals = $996.36       $1,076.1990   $1,076.21   $1,076.20   $1,076.20