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 $167.92   11.531%   $187.2829   $187.28   $187.30   $187.30  
  Purchase #2 $128.96   6.432%   $137.2547   $137.25   $137.25   $137.30  
  Purchase #3 $88.49   12.247%   $99.3274   $99.33   $99.35   $99.30  
  Purchase #4 $23.42   12.345%   $26.3112   $26.31   $26.30   $26.30  
  Purchase #5 $228.50   6.347%   $243.0029   $243.00   $243.00   $243.00  
  Purchase #6 $226.63   10.133%   $249.5944   $249.59   $249.60   $249.60  
  Purchase #7 $86.81   8.263%   $93.9831   $93.98   $94.00   $94.00  
  7 purchase totals = $950.73       $1,036.7566   $1,036.74   $1,036.80   $1,036.80