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 $172.39   13.363%   $195.4265   $195.43   $195.45   $195.40  
  Purchase #2 $9.97   8.468%   $10.8143   $10.81   $10.80   $10.80  
  Purchase #3 $39.62   9.467%   $43.3708   $43.37   $43.35   $43.40  
  Purchase #4 $246.49   13.829%   $280.5771   $280.58   $280.60   $280.60  
  Purchase #5 $237.77   4.541%   $248.5671   $248.57   $248.55   $248.60  
  Purchase #6 $90.85   5.697%   $96.0257   $96.03   $96.05   $96.00  
  Purchase #7 $10.53   4.623%   $11.0168   $11.02   $11.00   $11.00  
  7 purchase totals = $807.62       $885.7983   $885.81   $885.80   $885.80