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 $242.26   10.564%   $267.8523   $267.85   $267.85   $267.90  
  Purchase #2 $81.93   10.370%   $90.4261   $90.43   $90.45   $90.40  
  Purchase #3 $185.71   12.784%   $209.4512   $209.45   $209.45   $209.50  
  Purchase #4 $70.98   9.252%   $77.5471   $77.55   $77.55   $77.50  
  Purchase #5 $201.93   13.469%   $229.128   $229.13   $229.15   $229.10  
  Purchase #6 $210.55   10.327%   $232.2935   $232.29   $232.30   $232.30  
  Purchase #7 $80.61   5.772%   $85.2628   $85.26   $85.25   $85.30  
  7 purchase totals = $1,073.97       $1,191.9610   $1,191.96   $1,192.00   $1,192.00