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 $68.61   8.800%   $74.6477   $74.65   $74.65   $74.60  
  Purchase #2 $203.51   3.843%   $211.3309   $211.33   $211.35   $211.30  
  Purchase #3 $185.55   9.441%   $203.0678   $203.07   $203.05   $203.10  
  Purchase #4 $62.36   13.293%   $70.6495   $70.65   $70.65   $70.60  
  Purchase #5 $105.65   11.132%   $117.411   $117.41   $117.40   $117.40  
  Purchase #6 $68.41   9.231%   $74.7249   $74.72   $74.70   $74.70  
  Purchase #7 $202.98   10.351%   $223.9905   $223.99   $224.00   $224.00  
  7 purchase totals = $897.07       $975.8223   $975.82   $975.80   $975.70