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 $66.52   12.516%   $74.8456   $74.85   $74.85   $74.80  
  Purchase #2 $176.30   3.713%   $182.846   $182.85   $182.85   $182.80  
  Purchase #3 $188.69   9.172%   $205.9966   $206.00   $206.00   $206.00  
  Purchase #4 $223.79   8.190%   $242.1184   $242.12   $242.10   $242.10  
  Purchase #5 $34.98   10.535%   $38.6651   $38.67   $38.65   $38.70  
  Purchase #6 $239.33   3.651%   $248.0679   $248.07   $248.05   $248.10  
  Purchase #7 $21.72   13.815%   $24.7206   $24.72   $24.70   $24.70  
  7 purchase totals = $951.33       $1,017.2602   $1,017.28   $1,017.20   $1,017.20