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 $53.76   8.202%   $58.1694   $58.17   $58.15   $58.20  
  Purchase #2 $167.68   8.129%   $181.3107   $181.31   $181.30   $181.30  
  Purchase #3 $85.88   3.803%   $89.146   $89.15   $89.15   $89.10  
  Purchase #4 $220.48   13.233%   $249.6561   $249.66   $249.65   $249.70  
  Purchase #5 $231.64   8.831%   $252.0961   $252.10   $252.10   $252.10  
  Purchase #6 $170.60   6.280%   $181.3137   $181.31   $181.30   $181.30  
  Purchase #7 $125.94   10.727%   $139.4496   $139.45   $139.45   $139.40  
  7 purchase totals = $1,055.98       $1,151.1416   $1,151.15   $1,151.10   $1,151.10