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 $216.32   10.458%   $238.9427   $238.94   $238.95   $238.90  
  Purchase #2 $160.54   8.664%   $174.4492   $174.45   $174.45   $174.40  
  Purchase #3 $142.58   3.847%   $148.0651   $148.07   $148.05   $148.10  
  Purchase #4 $150.26   5.768%   $158.927   $158.93   $158.95   $158.90  
  Purchase #5 $152.35   13.407%   $172.7756   $172.78   $172.80   $172.80  
  Purchase #6 $160.62   8.605%   $174.4414   $174.44   $174.45   $174.40  
  Purchase #7 $5.31   8.797%   $5.7771   $5.78   $5.80   $5.80  
  7 purchase totals = $987.98       $1,073.3781   $1,073.39   $1,073.45   $1,073.30