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 $235.85   12.262%   $264.7699   $264.77   $264.75   $264.80  
  Purchase #2 $24.75   8.712%   $26.9062   $26.91   $26.90   $26.90  
  Purchase #3 $132.66   13.757%   $150.91   $150.91   $150.90   $150.90  
  Purchase #4 $131.68   13.121%   $148.9577   $148.96   $148.95   $149.00  
  Purchase #5 $114.62   12.340%   $128.7641   $128.76   $128.75   $128.80  
  Purchase #6 $166.29   4.714%   $174.1289   $174.13   $174.15   $174.10  
  Purchase #7 $228.84   13.678%   $260.1407   $260.14   $260.15   $260.10  
  7 purchase totals = $1,034.69       $1,154.5775   $1,154.58   $1,154.55   $1,154.60