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 $53.51   10.136%   $58.9338   $58.93   $58.95   $58.90  
  Purchase #2 $246.60   5.681%   $260.6093   $260.61   $260.60   $260.60  
  Purchase #3 $46.99   10.821%   $52.0748   $52.07   $52.05   $52.10  
  Purchase #4 $242.28   10.216%   $267.0313   $267.03   $267.05   $267.00  
  Purchase #5 $201.81   11.674%   $225.3693   $225.37   $225.35   $225.40  
  Purchase #6 $116.45   9.846%   $127.9157   $127.92   $127.90   $127.90  
  Purchase #7 $188.56   6.774%   $201.3331   $201.33   $201.35   $201.30  
  7 purchase totals = $1,096.20       $1,193.2673   $1,193.26   $1,193.25   $1,193.20