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 $35.87   7.489%   $38.5563   $38.56   $38.55   $38.60  
  Purchase #2 $210.85   5.642%   $222.7462   $222.75   $222.75   $222.70  
  Purchase #3 $82.95   5.156%   $87.2269   $87.23   $87.25   $87.20  
  Purchase #4 $197.91   5.762%   $209.3136   $209.31   $209.30   $209.30  
  Purchase #5 $212.81   11.781%   $237.8811   $237.88   $237.90   $237.90  
  Purchase #6 $150.93   11.229%   $167.8779   $167.88   $167.90   $167.90  
  Purchase #7 $213.79   13.710%   $243.1006   $243.10   $243.10   $243.10  
  7 purchase totals = $1,105.11       $1,206.7026   $1,206.71   $1,206.75   $1,206.70