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 $152.64   6.361%   $162.3494   $162.35   $162.35   $162.30  
  Purchase #2 $198.87   10.832%   $220.4116   $220.41   $220.40   $220.40  
  Purchase #3 $153.28   10.729%   $169.7254   $169.73   $169.75   $169.70  
  Purchase #4 $63.31   6.713%   $67.56   $67.56   $67.55   $67.60  
  Purchase #5 $56.49   6.406%   $60.1087   $60.11   $60.10   $60.10  
  Purchase #6 $181.59   3.617%   $188.1581   $188.16   $188.15   $188.20  
  Purchase #7 $112.95   9.793%   $124.0112   $124.01   $124.00   $124.00  
  7 purchase totals = $919.13       $992.3244   $992.33   $992.30   $992.30