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 $49.40   7.231%   $52.9721   $52.97   $52.95   $53.00  
  Purchase #2 $223.39   11.789%   $249.7254   $249.73   $249.75   $249.70  
  Purchase #3 $224.29   9.693%   $246.0304   $246.03   $246.05   $246.00  
  Purchase #4 $202.44   13.145%   $229.0507   $229.05   $229.05   $229.10  
  Purchase #5 $67.39   5.117%   $70.8383   $70.84   $70.85   $70.80  
  Purchase #6 $63.81   12.784%   $71.9675   $71.97   $71.95   $72.00  
  Purchase #7 $166.70   9.440%   $182.4365   $182.44   $182.45   $182.40  
  7 purchase totals = $997.42       $1,103.0209   $1,103.03   $1,103.05   $1,103.00