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 $90.73   6.548%   $96.671   $96.67   $96.65   $96.70  
  Purchase #2 $26.89   11.550%   $29.9958   $30.00   $30.00   $30.00  
  Purchase #3 $97.62   6.310%   $103.7798   $103.78   $103.80   $103.80  
  Purchase #4 $162.65   5.352%   $171.355   $171.36   $171.35   $171.40  
  Purchase #5 $246.93   4.444%   $257.9036   $257.90   $257.90   $257.90  
  Purchase #6 $153.40   12.383%   $172.3955   $172.40   $172.40   $172.40  
  Purchase #7 $238.99   12.650%   $269.2222   $269.22   $269.20   $269.20  
  7 purchase totals = $1,017.21       $1,101.3229   $1,101.33   $1,101.30   $1,101.40