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 $235.44   13.202%   $266.5228   $266.52   $266.50   $266.50  
  Purchase #2 $223.85   9.291%   $244.6479   $244.65   $244.65   $244.60  
  Purchase #3 $27.98   9.354%   $30.5972   $30.60   $30.60   $30.60  
  Purchase #4 $147.74   8.510%   $160.3127   $160.31   $160.30   $160.30  
  Purchase #5 $192.85   10.423%   $212.9508   $212.95   $212.95   $213.00  
  Purchase #6 $220.29   5.141%   $231.6151   $231.62   $231.60   $231.60  
  Purchase #7 $196.98   13.457%   $223.4876   $223.49   $223.50   $223.50  
  7 purchase totals = $1,245.13       $1,370.1341   $1,370.14   $1,370.10   $1,370.10