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 $113.38   5.227%   $119.3064   $119.31   $119.30   $119.30  
  Purchase #2 $218.28   10.572%   $241.3566   $241.36   $241.35   $241.40  
  Purchase #3 $203.41   4.192%   $211.9369   $211.94   $211.95   $211.90  
  Purchase #4 $54.81   5.692%   $57.9298   $57.93   $57.95   $57.90  
  Purchase #5 $122.73   6.487%   $130.6915   $130.69   $130.70   $130.70  
  Purchase #6 $38.54   13.717%   $43.8265   $43.83   $43.85   $43.80  
  Purchase #7 $244.52   8.595%   $265.5365   $265.54   $265.55   $265.50  
  7 purchase totals = $995.67       $1,070.5842   $1,070.60   $1,070.65   $1,070.50