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 $59.88   13.609%   $68.0291   $68.03   $68.05   $68.00  
  Purchase #2 $130.50   12.566%   $146.8986   $146.90   $146.90   $146.90  
  Purchase #3 $133.79   11.318%   $148.9324   $148.93   $148.95   $148.90  
  Purchase #4 $203.87   6.312%   $216.7383   $216.74   $216.75   $216.70  
  Purchase #5 $189.39   5.771%   $200.3197   $200.32   $200.30   $200.30  
  Purchase #6 $228.46   6.520%   $243.3556   $243.36   $243.35   $243.40  
  Purchase #7 $53.39   3.467%   $55.241   $55.24   $55.25   $55.20  
  7 purchase totals = $999.28       $1,079.5147   $1,079.52   $1,079.55   $1,079.40