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 $92.67   7.251%   $99.3895   $99.39   $99.40   $99.40  
  Purchase #2 $231.32   8.225%   $250.3461   $250.35   $250.35   $250.30  
  Purchase #3 $245.36   7.535%   $263.8479   $263.85   $263.85   $263.80  
  Purchase #4 $201.95   9.199%   $220.5274   $220.53   $220.55   $220.50  
  Purchase #5 $52.32   7.531%   $56.2602   $56.26   $56.25   $56.30  
  Purchase #6 $8.53   12.859%   $9.6269   $9.63   $9.65   $9.60  
  Purchase #7 $89.38   7.332%   $95.9333   $95.93   $95.95   $95.90  
  7 purchase totals = $921.53       $995.9313   $995.94   $996.00   $995.80