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 $83.98   5.413%   $88.5258   $88.53   $88.55   $88.50  
  Purchase #2 $123.85   6.363%   $131.7306   $131.73   $131.75   $131.70  
  Purchase #3 $224.48   6.777%   $239.693   $239.69   $239.70   $239.70  
  Purchase #4 $142.45   3.821%   $147.893   $147.89   $147.90   $147.90  
  Purchase #5 $16.95   3.653%   $17.5692   $17.57   $17.55   $17.60  
  Purchase #6 $165.80   11.481%   $184.8355   $184.84   $184.85   $184.80  
  Purchase #7 $173.79   12.405%   $195.3486   $195.35   $195.35   $195.30  
  7 purchase totals = $931.30       $1,005.5957   $1,005.60   $1,005.65   $1,005.50