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 $214.75   13.451%   $243.636   $243.64   $243.65   $243.60  
  Purchase #2 $81.44   8.573%   $88.4219   $88.42   $88.40   $88.40  
  Purchase #3 $14.78   4.621%   $15.463   $15.46   $15.45   $15.50  
  Purchase #4 $246.34   7.583%   $265.02   $265.02   $265.00   $265.00  
  Purchase #5 $82.65   8.170%   $89.4025   $89.40   $89.40   $89.40  
  Purchase #6 $121.87   9.582%   $133.5476   $133.55   $133.55   $133.50  
  Purchase #7 $212.38   9.763%   $233.1147   $233.11   $233.10   $233.10  
  7 purchase totals = $974.21       $1,068.6057   $1,068.60   $1,068.55   $1,068.50