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 $34.31   3.761%   $35.6004   $35.60   $35.60   $35.60  
  Purchase #2 $223.39   9.732%   $245.1303   $245.13   $245.15   $245.10  
  Purchase #3 $159.55   3.802%   $165.6161   $165.62   $165.60   $165.60  
  Purchase #4 $171.65   8.468%   $186.1853   $186.19   $186.20   $186.20  
  Purchase #5 $32.30   7.828%   $34.8284   $34.83   $34.85   $34.80  
  Purchase #6 $187.94   8.874%   $204.6178   $204.62   $204.60   $204.60  
  Purchase #7 $55.72   3.444%   $57.639   $57.64   $57.65   $57.60  
  7 purchase totals = $864.86       $929.6173   $929.63   $929.65   $929.50