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 $225.91   3.711%   $234.2935   $234.29   $234.30   $234.30  
  Purchase #2 $230.94   10.397%   $254.9508   $254.95   $254.95   $255.00  
  Purchase #3 $79.42   9.844%   $87.2381   $87.24   $87.25   $87.20  
  Purchase #4 $213.71   10.306%   $235.735   $235.74   $235.75   $235.70  
  Purchase #5 $78.88   7.529%   $84.8189   $84.82   $84.80   $84.80  
  Purchase #6 $56.47   11.391%   $62.9025   $62.90   $62.90   $62.90  
  Purchase #7 $48.50   8.384%   $52.5662   $52.57   $52.55   $52.60  
  7 purchase totals = $933.83       $1,012.5050   $1,012.51   $1,012.50   $1,012.50