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 $81.71   6.468%   $86.995   $87.00   $87.00   $87.00  
  Purchase #2 $225.34   3.391%   $232.9813   $232.98   $233.00   $233.00  
  Purchase #3 $123.81   3.433%   $128.0604   $128.06   $128.05   $128.10  
  Purchase #4 $129.74   9.187%   $141.6592   $141.66   $141.65   $141.70  
  Purchase #5 $85.71   12.316%   $96.266   $96.27   $96.25   $96.30  
  Purchase #6 $240.69   4.648%   $251.8773   $251.88   $251.90   $251.90  
  Purchase #7 $104.85   13.170%   $118.6587   $118.66   $118.65   $118.70  
  7 purchase totals = $991.85       $1,056.4979   $1,056.51   $1,056.50   $1,056.70