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 $124.29   4.864%   $130.3355   $130.34   $130.35   $130.30  
  Purchase #2 $235.84   13.151%   $266.8553   $266.86   $266.85   $266.90  
  Purchase #3 $162.51   11.317%   $180.9013   $180.90   $180.90   $180.90  
  Purchase #4 $60.80   8.215%   $65.7947   $65.79   $65.80   $65.80  
  Purchase #5 $65.64   4.557%   $68.6312   $68.63   $68.65   $68.60  
  Purchase #6 $185.90   4.734%   $194.7005   $194.70   $194.70   $194.70  
  Purchase #7 $178.77   3.806%   $185.574   $185.57   $185.55   $185.60  
  7 purchase totals = $1,013.75       $1,092.7925   $1,092.79   $1,092.80   $1,092.80