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 $20.55   5.372%   $21.6539   $21.65   $21.65   $21.70  
  Purchase #2 $233.40   7.551%   $251.024   $251.02   $251.00   $251.00  
  Purchase #3 $32.84   13.685%   $37.3342   $37.33   $37.35   $37.30  
  Purchase #4 $64.66   10.675%   $71.5625   $71.56   $71.55   $71.60  
  Purchase #5 $141.70   10.774%   $156.9668   $156.97   $156.95   $157.00  
  Purchase #6 $144.54   3.599%   $149.742   $149.74   $149.75   $149.70  
  Purchase #7 $147.84   5.151%   $155.4552   $155.46   $155.45   $155.50  
  7 purchase totals = $785.53       $843.7386   $843.73   $843.70   $843.80