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 $242.69   5.760%   $256.6689   $256.67   $256.65   $256.70  
  Purchase #2 $179.62   12.431%   $201.9486   $201.95   $201.95   $201.90  
  Purchase #3 $37.53   10.702%   $41.5465   $41.55   $41.55   $41.50  
  Purchase #4 $57.89   11.635%   $64.6255   $64.63   $64.65   $64.60  
  Purchase #5 $59.62   9.112%   $65.0526   $65.05   $65.05   $65.10  
  Purchase #6 $211.41   10.206%   $232.9865   $232.99   $233.00   $233.00  
  Purchase #7 $165.96   8.661%   $180.3338   $180.33   $180.35   $180.30  
  7 purchase totals = $954.72       $1,043.1624   $1,043.17   $1,043.20   $1,043.10