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 $234.85   5.624%   $248.058   $248.06   $248.05   $248.10  
  Purchase #2 $30.94   7.452%   $33.2456   $33.25   $33.25   $33.20  
  Purchase #3 $185.52   3.495%   $192.0039   $192.00   $192.00   $192.00  
  Purchase #4 $69.55   7.779%   $74.9603   $74.96   $74.95   $75.00  
  Purchase #5 $132.39   13.679%   $150.4996   $150.50   $150.50   $150.50  
  Purchase #6 $164.81   9.833%   $181.0158   $181.02   $181.00   $181.00  
  Purchase #7 $191.33   4.321%   $199.5974   $199.60   $199.60   $199.60  
  7 purchase totals = $1,009.39       $1,079.3806   $1,079.39   $1,079.35   $1,079.40