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 $239.77   11.377%   $267.0486   $267.05   $267.05   $267.00  
  Purchase #2 $236.41   8.567%   $256.6632   $256.66   $256.65   $256.70  
  Purchase #3 $5.55   10.135%   $6.1125   $6.11   $6.10   $6.10  
  Purchase #4 $50.92   6.627%   $54.2945   $54.29   $54.30   $54.30  
  Purchase #5 $244.44   3.565%   $253.1543   $253.15   $253.15   $253.20  
  Purchase #6 $59.67   8.585%   $64.7927   $64.79   $64.80   $64.80  
  Purchase #7 $189.86   6.165%   $201.5649   $201.56   $201.55   $201.60  
  7 purchase totals = $1,026.62       $1,103.6307   $1,103.61   $1,103.60   $1,103.70