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 $41.74   6.712%   $44.5416   $44.54   $44.55   $44.50  
  Purchase #2 $201.42   12.197%   $225.9872   $225.99   $226.00   $226.00  
  Purchase #3 $248.88   4.613%   $260.3608   $260.36   $260.35   $260.40  
  Purchase #4 $19.52   9.449%   $21.3644   $21.36   $21.35   $21.40  
  Purchase #5 $59.69   13.456%   $67.7219   $67.72   $67.70   $67.70  
  Purchase #6 $170.68   10.204%   $188.0962   $188.10   $188.10   $188.10  
  Purchase #7 $208.88   9.301%   $228.3079   $228.31   $228.30   $228.30  
  7 purchase totals = $950.81       $1,036.3800   $1,036.38   $1,036.35   $1,036.40