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 $83.31   6.352%   $88.6019   $88.60   $88.60   $88.60  
  Purchase #2 $221.93   11.401%   $247.2322   $247.23   $247.25   $247.20  
  Purchase #3 $215.68   7.418%   $231.6791   $231.68   $231.70   $231.70  
  Purchase #4 $202.44   6.439%   $215.4751   $215.48   $215.50   $215.50  
  Purchase #5 $31.72   12.124%   $35.5657   $35.57   $35.55   $35.60  
  Purchase #6 $147.89   3.637%   $153.2688   $153.27   $153.25   $153.30  
  Purchase #7 $59.33   8.321%   $64.2668   $64.27   $64.25   $64.30  
  7 purchase totals = $962.30       $1,036.0896   $1,036.10   $1,036.10   $1,036.20