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 $120.63   7.745%   $129.9728   $129.97   $129.95   $130.00  
  Purchase #2 $103.73   7.217%   $111.2162   $111.22   $111.20   $111.20  
  Purchase #3 $207.36   6.724%   $221.3029   $221.30   $221.30   $221.30  
  Purchase #4 $212.55   6.761%   $226.9205   $226.92   $226.90   $226.90  
  Purchase #5 $109.81   9.478%   $120.2178   $120.22   $120.20   $120.20  
  Purchase #6 $96.92   10.753%   $107.3418   $107.34   $107.35   $107.30  
  Purchase #7 $153.60   13.788%   $174.7784   $174.78   $174.80   $174.80  
  7 purchase totals = $1,004.60       $1,091.7504   $1,091.75   $1,091.70   $1,091.70