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 $45.91   9.637%   $50.3343   $50.33   $50.35   $50.30  
  Purchase #2 $242.28   4.155%   $252.3467   $252.35   $252.35   $252.30  
  Purchase #3 $33.56   6.310%   $35.6776   $35.68   $35.70   $35.70  
  Purchase #4 $235.54   9.547%   $258.027   $258.03   $258.05   $258.00  
  Purchase #5 $127.52   4.811%   $133.655   $133.66   $133.65   $133.70  
  Purchase #6 $241.93   13.305%   $274.1188   $274.12   $274.10   $274.10  
  Purchase #7 $70.60   5.688%   $74.6157   $74.62   $74.60   $74.60  
  7 purchase totals = $997.34       $1,078.7751   $1,078.79   $1,078.80   $1,078.70