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 $56.42   6.363%   $60.01   $60.01   $60.00   $60.00  
  Purchase #2 $203.93   4.248%   $212.5929   $212.59   $212.60   $212.60  
  Purchase #3 $160.61   9.201%   $175.3877   $175.39   $175.40   $175.40  
  Purchase #4 $84.64   12.586%   $95.2928   $95.29   $95.30   $95.30  
  Purchase #5 $89.53   6.792%   $95.6109   $95.61   $95.60   $95.60  
  Purchase #6 $121.91   13.639%   $138.5373   $138.54   $138.55   $138.50  
  Purchase #7 $230.91   3.675%   $239.3959   $239.40   $239.40   $239.40  
  7 purchase totals = $947.95       $1,016.8275   $1,016.83   $1,016.85   $1,016.80