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 $110.79   10.291%   $122.1914   $122.19   $122.20   $122.20  
  Purchase #2 $206.99   10.310%   $228.3307   $228.33   $228.35   $228.30  
  Purchase #3 $54.83   3.743%   $56.8823   $56.88   $56.90   $56.90  
  Purchase #4 $162.78   5.261%   $171.3439   $171.34   $171.35   $171.30  
  Purchase #5 $161.59   9.180%   $176.424   $176.42   $176.40   $176.40  
  Purchase #6 $171.72   12.656%   $193.4529   $193.45   $193.45   $193.50  
  Purchase #7 $236.68   5.129%   $248.8193   $248.82   $248.80   $248.80  
  7 purchase totals = $1,105.38       $1,197.4445   $1,197.43   $1,197.45   $1,197.40