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 $228.92   9.611%   $250.9215   $250.92   $250.90   $250.90  
  Purchase #2 $60.58   13.757%   $68.914   $68.91   $68.90   $68.90  
  Purchase #3 $101.80   9.546%   $111.5178   $111.52   $111.50   $111.50  
  Purchase #4 $118.36   6.288%   $125.8025   $125.80   $125.80   $125.80  
  Purchase #5 $188.75   11.608%   $210.6601   $210.66   $210.65   $210.70  
  Purchase #6 $214.65   5.489%   $226.4321   $226.43   $226.45   $226.40  
  Purchase #7 $228.69   12.851%   $258.079   $258.08   $258.10   $258.10  
  7 purchase totals = $1,141.75       $1,252.3270   $1,252.32   $1,252.30   $1,252.30