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 $107.27   10.721%   $118.7704   $118.77   $118.75   $118.80  
  Purchase #2 $241.28   13.409%   $273.6332   $273.63   $273.65   $273.60  
  Purchase #3 $191.97   4.761%   $201.1097   $201.11   $201.10   $201.10  
  Purchase #4 $24.35   13.360%   $27.6032   $27.60   $27.60   $27.60  
  Purchase #5 $36.77   4.219%   $38.3213   $38.32   $38.30   $38.30  
  Purchase #6 $130.73   5.286%   $137.6404   $137.64   $137.65   $137.60  
  Purchase #7 $235.94   7.619%   $253.9163   $253.92   $253.90   $253.90  
  7 purchase totals = $968.31       $1,050.9945   $1,050.99   $1,050.95   $1,050.90