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 $228.81   6.482%   $243.6415   $243.64   $243.65   $243.60  
  Purchase #2 $206.31   7.721%   $222.2392   $222.24   $222.25   $222.20  
  Purchase #3 $58.43   10.255%   $64.422   $64.42   $64.40   $64.40  
  Purchase #4 $195.34   8.113%   $211.1879   $211.19   $211.20   $211.20  
  Purchase #5 $200.90   12.712%   $226.4384   $226.44   $226.45   $226.40  
  Purchase #6 $64.87   3.761%   $67.3098   $67.31   $67.30   $67.30  
  Purchase #7 $67.30   7.322%   $72.2277   $72.23   $72.25   $72.20  
  7 purchase totals = $1,021.96       $1,107.4665   $1,107.47   $1,107.50   $1,107.30