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 $224.87   10.124%   $247.6358   $247.64   $247.65   $247.60  
  Purchase #2 $158.33   8.413%   $171.6503   $171.65   $171.65   $171.70  
  Purchase #3 $21.61   6.420%   $22.9974   $23.00   $23.00   $23.00  
  Purchase #4 $206.99   10.429%   $228.577   $228.58   $228.60   $228.60  
  Purchase #5 $94.47   12.867%   $106.6255   $106.63   $106.65   $106.60  
  Purchase #6 $211.40   9.743%   $231.9967   $232.00   $232.00   $232.00  
  Purchase #7 $103.45   3.725%   $107.3035   $107.30   $107.30   $107.30  
  7 purchase totals = $1,021.12       $1,116.7862   $1,116.80   $1,116.85   $1,116.80