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 $195.76   6.658%   $208.7937   $208.79   $208.80   $208.80  
  Purchase #2 $23.36   4.133%   $24.3255   $24.33   $24.35   $24.30  
  Purchase #3 $16.28   7.774%   $17.5456   $17.55   $17.55   $17.50  
  Purchase #4 $81.51   4.392%   $85.0899   $85.09   $85.10   $85.10  
  Purchase #5 $45.82   10.709%   $50.7269   $50.73   $50.75   $50.70  
  Purchase #6 $225.63   6.814%   $241.0044   $241.00   $241.00   $241.00  
  Purchase #7 $203.89   9.135%   $222.5154   $222.52   $222.50   $222.50  
  7 purchase totals = $792.25       $850.0014   $850.01   $850.05   $849.90