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 $192.84   6.643%   $205.6504   $205.65   $205.65   $205.70  
  Purchase #2 $169.73   9.576%   $185.9833   $185.98   $186.00   $186.00  
  Purchase #3 $103.55   13.650%   $117.6846   $117.68   $117.70   $117.70  
  Purchase #4 $228.67   11.256%   $254.4091   $254.41   $254.40   $254.40  
  Purchase #5 $40.79   13.320%   $46.2232   $46.22   $46.20   $46.20  
  Purchase #6 $168.50   7.837%   $181.7053   $181.71   $181.70   $181.70  
  Purchase #7 $69.36   5.221%   $72.9813   $72.98   $73.00   $73.00  
  7 purchase totals = $973.44       $1,064.6372   $1,064.63   $1,064.65   $1,064.70