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 $138.80   11.359%   $154.5663   $154.57   $154.55   $154.60  
  Purchase #2 $75.46   3.143%   $77.8317   $77.83   $77.85   $77.80  
  Purchase #3 $173.34   10.859%   $192.163   $192.16   $192.15   $192.20  
  Purchase #4 $99.61   7.139%   $106.7212   $106.72   $106.70   $106.70  
  Purchase #5 $225.62   4.114%   $234.902   $234.90   $234.90   $234.90  
  Purchase #6 $165.58   8.556%   $179.747   $179.75   $179.75   $179.70  
  Purchase #7 $5.70   8.620%   $6.1913   $6.19   $6.20   $6.20  
  7 purchase totals = $884.11       $952.1225   $952.12   $952.10   $952.10