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 $87.78   8.189%   $94.9683   $94.97   $94.95   $95.00  
  Purchase #2 $5.91   3.475%   $6.1154   $6.12   $6.10   $6.10  
  Purchase #3 $139.92   11.468%   $155.966   $155.97   $155.95   $156.00  
  Purchase #4 $56.72   7.535%   $60.9939   $60.99   $61.00   $61.00  
  Purchase #5 $60.71   8.184%   $65.6785   $65.68   $65.70   $65.70  
  Purchase #6 $22.56   11.206%   $25.0881   $25.09   $25.10   $25.10  
  Purchase #7 $157.74   8.316%   $170.8577   $170.86   $170.85   $170.90  
  7 purchase totals = $531.34       $579.6679   $579.68   $579.65   $579.80