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 $202.44   4.374%   $211.2947   $211.29   $211.30   $211.30  
  Purchase #2 $242.65   8.851%   $264.127   $264.13   $264.15   $264.10  
  Purchase #3 $78.95   11.538%   $88.0593   $88.06   $88.05   $88.10  
  Purchase #4 $226.51   13.693%   $257.526   $257.53   $257.55   $257.50  
  Purchase #5 $170.93   12.593%   $192.4552   $192.46   $192.45   $192.50  
  Purchase #6 $55.68   13.810%   $63.3694   $63.37   $63.35   $63.40  
  Purchase #7 $18.32   6.618%   $19.5324   $19.53   $19.55   $19.50  
  7 purchase totals = $995.48       $1,096.3640   $1,096.37   $1,096.40   $1,096.40