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 $49.83   4.453%   $52.0489   $52.05   $52.05   $52.00  
  Purchase #2 $233.72   5.838%   $247.3646   $247.36   $247.35   $247.40  
  Purchase #3 $165.99   5.516%   $175.146   $175.15   $175.15   $175.10  
  Purchase #4 $98.89   13.301%   $112.0434   $112.04   $112.05   $112.00  
  Purchase #5 $102.37   8.214%   $110.7787   $110.78   $110.80   $110.80  
  Purchase #6 $228.91   12.464%   $257.4413   $257.44   $257.45   $257.40  
  Purchase #7 $49.67   11.556%   $55.4099   $55.41   $55.40   $55.40  
  7 purchase totals = $929.38       $1,010.2328   $1,010.23   $1,010.25   $1,010.10