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 $227.64   3.721%   $236.1105   $236.11   $236.10   $236.10  
  Purchase #2 $173.87   4.599%   $181.8663   $181.87   $181.85   $181.90  
  Purchase #3 $55.25   4.561%   $57.77   $57.77   $57.75   $57.80  
  Purchase #4 $188.82   8.666%   $205.1831   $205.18   $205.20   $205.20  
  Purchase #5 $233.56   4.363%   $243.7502   $243.75   $243.75   $243.80  
  Purchase #6 $12.47   6.328%   $13.2591   $13.26   $13.25   $13.30  
  Purchase #7 $66.49   11.366%   $74.0473   $74.05   $74.05   $74.00  
  7 purchase totals = $958.10       $1,011.9865   $1,011.99   $1,011.95   $1,012.10