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 $9.30   13.677%   $10.572   $10.57   $10.55   $10.60  
  Purchase #2 $133.45   11.560%   $148.8768   $148.88   $148.90   $148.90  
  Purchase #3 $228.89   6.439%   $243.6282   $243.63   $243.65   $243.60  
  Purchase #4 $133.31   10.614%   $147.4595   $147.46   $147.45   $147.50  
  Purchase #5 $243.66   6.829%   $260.2995   $260.30   $260.30   $260.30  
  Purchase #6 $187.62   10.418%   $207.1663   $207.17   $207.15   $207.20  
  Purchase #7 $165.91   8.270%   $179.6308   $179.63   $179.65   $179.60  
  7 purchase totals = $1,102.14       $1,197.6331   $1,197.64   $1,197.65   $1,197.70