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 $194.68   5.119%   $204.6457   $204.65   $204.65   $204.60  
  Purchase #2 $32.55   12.756%   $36.7021   $36.70   $36.70   $36.70  
  Purchase #3 $226.98   10.756%   $251.394   $251.39   $251.40   $251.40  
  Purchase #4 $149.54   4.360%   $156.0599   $156.06   $156.05   $156.10  
  Purchase #5 $113.66   6.548%   $121.1025   $121.10   $121.10   $121.10  
  Purchase #6 $156.71   7.381%   $168.2768   $168.28   $168.30   $168.30  
  Purchase #7 $107.27   4.203%   $111.7786   $111.78   $111.80   $111.80  
  7 purchase totals = $981.39       $1,049.9596   $1,049.96   $1,050.00   $1,050.00