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 $56.92   3.111%   $58.6908   $58.69   $58.70   $58.70  
  Purchase #2 $245.98   13.159%   $278.3485   $278.35   $278.35   $278.30  
  Purchase #3 $94.92   10.323%   $104.7186   $104.72   $104.70   $104.70  
  Purchase #4 $63.42   11.618%   $70.7881   $70.79   $70.80   $70.80  
  Purchase #5 $219.99   11.795%   $245.9378   $245.94   $245.95   $245.90  
  Purchase #6 $248.27   6.689%   $264.8768   $264.88   $264.90   $264.90  
  Purchase #7 $128.68   9.465%   $140.8596   $140.86   $140.85   $140.90  
  7 purchase totals = $1,058.18       $1,164.2202   $1,164.23   $1,164.25   $1,164.20