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 $241.47   9.816%   $265.1727   $265.17   $265.15   $265.20  
  Purchase #2 $184.81   5.383%   $194.7583   $194.76   $194.75   $194.80  
  Purchase #3 $60.67   13.377%   $68.7858   $68.79   $68.80   $68.80  
  Purchase #4 $165.39   13.632%   $187.936   $187.94   $187.95   $187.90  
  Purchase #5 $24.90   10.498%   $27.514   $27.51   $27.50   $27.50  
  Purchase #6 $186.60   13.489%   $211.7705   $211.77   $211.75   $211.80  
  Purchase #7 $34.52   12.343%   $38.7808   $38.78   $38.80   $38.80  
  7 purchase totals = $898.36       $994.7181   $994.72   $994.70   $994.80