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 $91.52   5.178%   $96.2589   $96.26   $96.25   $96.30  
  Purchase #2 $236.88   8.765%   $257.6425   $257.64   $257.65   $257.60  
  Purchase #3 $209.68   12.163%   $235.1834   $235.18   $235.20   $235.20  
  Purchase #4 $61.86   7.346%   $66.4042   $66.40   $66.40   $66.40  
  Purchase #5 $189.82   7.254%   $203.5895   $203.59   $203.60   $203.60  
  Purchase #6 $6.92   5.651%   $7.311   $7.31   $7.30   $7.30  
  Purchase #7 $241.40   13.157%   $273.161   $273.16   $273.15   $273.20  
  7 purchase totals = $1,038.08       $1,139.5505   $1,139.54   $1,139.55   $1,139.60