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 $73.26   8.642%   $79.5911   $79.59   $79.60   $79.60  
  Purchase #2 $217.44   6.351%   $231.2496   $231.25   $231.25   $231.20  
  Purchase #3 $201.97   10.774%   $223.7302   $223.73   $223.75   $223.70  
  Purchase #4 $233.84   8.490%   $253.693   $253.69   $253.70   $253.70  
  Purchase #5 $207.50   6.302%   $220.5767   $220.58   $220.60   $220.60  
  Purchase #6 $138.40   10.758%   $153.2891   $153.29   $153.30   $153.30  
  Purchase #7 $218.98   7.421%   $235.2305   $235.23   $235.25   $235.20  
  7 purchase totals = $1,291.39       $1,397.3602   $1,397.36   $1,397.45   $1,397.30