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 $142.54   6.129%   $151.2763   $151.28   $151.30   $151.30  
  Purchase #2 $227.54   5.302%   $239.6042   $239.60   $239.60   $239.60  
  Purchase #3 $85.39   6.855%   $91.2435   $91.24   $91.25   $91.20  
  Purchase #4 $211.87   6.254%   $225.1203   $225.12   $225.10   $225.10  
  Purchase #5 $186.37   13.168%   $210.9112   $210.91   $210.90   $210.90  
  Purchase #6 $165.67   9.759%   $181.8377   $181.84   $181.85   $181.80  
  Purchase #7 $13.55   5.137%   $14.2461   $14.25   $14.25   $14.20  
  7 purchase totals = $1,032.93       $1,114.2393   $1,114.24   $1,114.25   $1,114.10