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 $123.86   8.352%   $134.2048   $134.20   $134.20   $134.20  
  Purchase #2 $166.45   10.286%   $183.571   $183.57   $183.55   $183.60  
  Purchase #3 $65.51   12.782%   $73.8835   $73.88   $73.90   $73.90  
  Purchase #4 $36.71   9.823%   $40.316   $40.32   $40.30   $40.30  
  Purchase #5 $161.50   7.440%   $173.5156   $173.52   $173.50   $173.50  
  Purchase #6 $212.97   8.837%   $231.7902   $231.79   $231.80   $231.80  
  Purchase #7 $215.82   4.682%   $225.9247   $225.92   $225.90   $225.90  
  7 purchase totals = $982.82       $1,063.2058   $1,063.20   $1,063.15   $1,063.20