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 $120.26   8.291%   $130.2308   $130.23   $130.25   $130.20  
  Purchase #2 $209.25   11.852%   $234.0503   $234.05   $234.05   $234.10  
  Purchase #3 $245.96   13.424%   $278.9777   $278.98   $279.00   $279.00  
  Purchase #4 $56.41   11.186%   $62.72   $62.72   $62.70   $62.70  
  Purchase #5 $107.91   11.330%   $120.1362   $120.14   $120.15   $120.10  
  Purchase #6 $150.35   10.542%   $166.1999   $166.20   $166.20   $166.20  
  Purchase #7 $55.35   11.464%   $61.6953   $61.70   $61.70   $61.70  
  7 purchase totals = $945.49       $1,054.0102   $1,054.02   $1,054.05   $1,054.00