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 $118.66   13.628%   $134.831   $134.83   $134.85   $134.80  
  Purchase #2 $74.34   4.262%   $77.5084   $77.51   $77.50   $77.50  
  Purchase #3 $64.59   5.488%   $68.1347   $68.13   $68.15   $68.10  
  Purchase #4 $173.32   3.136%   $178.7553   $178.76   $178.75   $178.80  
  Purchase #5 $249.64   9.454%   $273.241   $273.24   $273.25   $273.20  
  Purchase #6 $213.94   5.237%   $225.144   $225.14   $225.15   $225.10  
  Purchase #7 $98.29   7.415%   $105.5782   $105.58   $105.60   $105.60  
  7 purchase totals = $992.78       $1,063.1926   $1,063.19   $1,063.25   $1,063.10