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 $222.64   3.705%   $230.8888   $230.89   $230.90   $230.90  
  Purchase #2 $197.88   7.136%   $212.0007   $212.00   $212.00   $212.00  
  Purchase #3 $128.91   13.359%   $146.1311   $146.13   $146.15   $146.10  
  Purchase #4 $157.42   13.784%   $179.1188   $179.12   $179.10   $179.10  
  Purchase #5 $187.68   3.676%   $194.5791   $194.58   $194.60   $194.60  
  Purchase #6 $35.74   7.436%   $38.3976   $38.40   $38.40   $38.40  
  Purchase #7 $209.88   9.687%   $230.2111   $230.21   $230.20   $230.20  
  7 purchase totals = $1,140.15       $1,231.3272   $1,231.33   $1,231.35   $1,231.30