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 $110.71   10.787%   $122.6523   $122.65   $122.65   $122.70  
  Purchase #2 $219.99   6.751%   $234.8415   $234.84   $234.85   $234.80  
  Purchase #3 $14.92   10.331%   $16.4614   $16.46   $16.45   $16.50  
  Purchase #4 $199.41   11.505%   $222.3521   $222.35   $222.35   $222.40  
  Purchase #5 $6.37   8.737%   $6.9265   $6.93   $6.95   $6.90  
  Purchase #6 $114.40   3.548%   $118.4589   $118.46   $118.45   $118.50  
  Purchase #7 $250.72   8.661%   $272.4349   $272.43   $272.45   $272.40  
  7 purchase totals = $916.52       $994.1276   $994.12   $994.15   $994.20