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 $143.34   7.270%   $153.7608   $153.76   $153.75   $153.80  
  Purchase #2 $237.73   3.512%   $246.0791   $246.08   $246.10   $246.10  
  Purchase #3 $169.46   4.758%   $177.5229   $177.52   $177.50   $177.50  
  Purchase #4 $26.91   8.110%   $29.0924   $29.09   $29.10   $29.10  
  Purchase #5 $33.25   7.414%   $35.7152   $35.72   $35.70   $35.70  
  Purchase #6 $132.28   11.572%   $147.5874   $147.59   $147.60   $147.60  
  Purchase #7 $203.66   7.838%   $219.6229   $219.62   $219.60   $219.60  
  7 purchase totals = $946.63       $1,009.3807   $1,009.38   $1,009.35   $1,009.40