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 $63.88   9.513%   $69.9569   $69.96   $69.95   $70.00  
  Purchase #2 $230.97   11.826%   $258.2845   $258.28   $258.30   $258.30  
  Purchase #3 $142.29   3.502%   $147.273   $147.27   $147.25   $147.30  
  Purchase #4 $239.81   11.393%   $267.1316   $267.13   $267.15   $267.10  
  Purchase #5 $78.53   8.783%   $85.4273   $85.43   $85.45   $85.40  
  Purchase #6 $54.47   6.170%   $57.8308   $57.83   $57.85   $57.80  
  Purchase #7 $33.52   7.221%   $35.9405   $35.94   $35.95   $35.90  
  7 purchase totals = $843.47       $921.8446   $921.84   $921.90   $921.80