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 $247.71   7.874%   $267.2147   $267.21   $267.20   $267.20  
  Purchase #2 $232.34   11.658%   $259.4262   $259.43   $259.45   $259.40  
  Purchase #3 $57.52   13.861%   $65.4928   $65.49   $65.50   $65.50  
  Purchase #4 $123.36   13.251%   $139.7064   $139.71   $139.70   $139.70  
  Purchase #5 $220.92   9.645%   $242.2277   $242.23   $242.25   $242.20  
  Purchase #6 $5.73   3.385%   $5.924   $5.92   $5.90   $5.90  
  Purchase #7 $160.99   4.823%   $168.7545   $168.75   $168.75   $168.80  
  7 purchase totals = $1,048.57       $1,148.7463   $1,148.74   $1,148.75   $1,148.70