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 $147.62   10.212%   $162.695   $162.70   $162.70   $162.70  
  Purchase #2 $179.83   11.171%   $199.9188   $199.92   $199.90   $199.90  
  Purchase #3 $5.98   9.452%   $6.5452   $6.55   $6.55   $6.50  
  Purchase #4 $39.26   10.546%   $43.4004   $43.40   $43.40   $43.40  
  Purchase #5 $148.45   9.461%   $162.4949   $162.49   $162.50   $162.50  
  Purchase #6 $179.39   12.297%   $201.4496   $201.45   $201.45   $201.40  
  Purchase #7 $133.54   12.315%   $149.9855   $149.99   $150.00   $150.00  
  7 purchase totals = $834.07       $926.4894   $926.50   $926.50   $926.40