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 $71.93   7.310%   $77.1881   $77.19   $77.20   $77.20  
  Purchase #2 $195.57   4.418%   $204.2103   $204.21   $204.20   $204.20  
  Purchase #3 $16.72   5.700%   $17.673   $17.67   $17.65   $17.70  
  Purchase #4 $227.64   5.191%   $239.4568   $239.46   $239.45   $239.50  
  Purchase #5 $17.50   7.323%   $18.7815   $18.78   $18.80   $18.80  
  Purchase #6 $202.83   13.409%   $230.0275   $230.03   $230.05   $230.00  
  Purchase #7 $204.97   4.829%   $214.868   $214.87   $214.85   $214.90  
  7 purchase totals = $937.16       $1,002.2052   $1,002.21   $1,002.20   $1,002.30