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 $205.73   11.606%   $229.607   $229.61   $229.60   $229.60  
  Purchase #2 $59.83   5.424%   $63.0752   $63.08   $63.10   $63.10  
  Purchase #3 $244.90   11.552%   $273.1908   $273.19   $273.20   $273.20  
  Purchase #4 $112.52   6.702%   $120.0611   $120.06   $120.05   $120.10  
  Purchase #5 $109.32   12.423%   $122.9008   $122.90   $122.90   $122.90  
  Purchase #6 $152.37   9.351%   $166.6181   $166.62   $166.60   $166.60  
  Purchase #7 $95.82   5.198%   $100.8007   $100.80   $100.80   $100.80  
  7 purchase totals = $980.49       $1,076.2537   $1,076.26   $1,076.25   $1,076.30