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 $207.54   3.218%   $214.2186   $214.22   $214.20   $214.20  
  Purchase #2 $217.27   4.390%   $226.8082   $226.81   $226.80   $226.80  
  Purchase #3 $17.48   11.699%   $19.525   $19.53   $19.55   $19.50  
  Purchase #4 $59.34   5.753%   $62.7538   $62.75   $62.75   $62.80  
  Purchase #5 $202.33   10.306%   $223.1821   $223.18   $223.20   $223.20  
  Purchase #6 $163.41   6.555%   $174.1215   $174.12   $174.10   $174.10  
  Purchase #7 $125.39   4.286%   $130.7642   $130.76   $130.75   $130.80  
  7 purchase totals = $992.76       $1,051.3734   $1,051.37   $1,051.35   $1,051.40