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 $64.96   13.813%   $73.9329   $73.93   $73.95   $73.90  
  Purchase #2 $231.61   8.307%   $250.8498   $250.85   $250.85   $250.80  
  Purchase #3 $38.49   8.865%   $41.9021   $41.90   $41.90   $41.90  
  Purchase #4 $122.61   11.814%   $137.0951   $137.10   $137.10   $137.10  
  Purchase #5 $169.79   12.799%   $191.5214   $191.52   $191.50   $191.50  
  Purchase #6 $33.95   8.264%   $36.7556   $36.76   $36.75   $36.80  
  Purchase #7 $88.69   3.326%   $91.6398   $91.64   $91.65   $91.60  
  7 purchase totals = $750.10       $823.6967   $823.70   $823.70   $823.60