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 $175.41   12.123%   $196.675   $196.68   $196.70   $196.70  
  Purchase #2 $103.58   4.689%   $108.4369   $108.44   $108.45   $108.40  
  Purchase #3 $104.64   8.863%   $113.9142   $113.91   $113.90   $113.90  
  Purchase #4 $165.78   3.122%   $170.9557   $170.96   $170.95   $171.00  
  Purchase #5 $45.49   10.807%   $50.4061   $50.41   $50.40   $50.40  
  Purchase #6 $55.88   9.225%   $61.0349   $61.03   $61.05   $61.00  
  Purchase #7 $235.33   7.747%   $253.561   $253.56   $253.55   $253.60  
  7 purchase totals = $886.11       $954.9838   $954.99   $955.00   $955.00