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 $127.71   13.820%   $145.3595   $145.36   $145.35   $145.40  
  Purchase #2 $162.39   11.113%   $180.4364   $180.44   $180.45   $180.40  
  Purchase #3 $221.78   11.709%   $247.7482   $247.75   $247.75   $247.70  
  Purchase #4 $181.79   10.115%   $200.1781   $200.18   $200.20   $200.20  
  Purchase #5 $47.94   10.436%   $52.943   $52.94   $52.95   $52.90  
  Purchase #6 $222.49   11.541%   $248.1676   $248.17   $248.15   $248.20  
  Purchase #7 $96.65   10.840%   $107.1269   $107.13   $107.15   $107.10  
  7 purchase totals = $1,060.75       $1,181.9597   $1,181.97   $1,182.00   $1,181.90