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 $85.74   8.813%   $93.2963   $93.30   $93.30   $93.30  
  Purchase #2 $152.57   12.485%   $171.6184   $171.62   $171.60   $171.60  
  Purchase #3 $205.53   6.261%   $218.3982   $218.40   $218.40   $218.40  
  Purchase #4 $16.54   7.462%   $17.7742   $17.77   $17.75   $17.80  
  Purchase #5 $193.45   5.830%   $204.7281   $204.73   $204.75   $204.70  
  Purchase #6 $174.98   3.467%   $181.0466   $181.05   $181.05   $181.00  
  Purchase #7 $147.85   6.350%   $157.2385   $157.24   $157.25   $157.20  
  7 purchase totals = $976.66       $1,044.1003   $1,044.11   $1,044.10   $1,044.00