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 $46.44   5.385%   $48.9408   $48.94   $48.95   $48.90  
  Purchase #2 $219.95   6.754%   $234.8054   $234.81   $234.80   $234.80  
  Purchase #3 $139.33   11.286%   $155.0548   $155.05   $155.05   $155.10  
  Purchase #4 $88.61   7.115%   $94.9146   $94.91   $94.90   $94.90  
  Purchase #5 $63.70   7.244%   $68.3144   $68.31   $68.30   $68.30  
  Purchase #6 $203.76   12.562%   $229.3563   $229.36   $229.35   $229.40  
  Purchase #7 $179.61   4.744%   $188.1307   $188.13   $188.15   $188.10  
  7 purchase totals = $941.40       $1,019.5170   $1,019.51   $1,019.50   $1,019.50