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 $200.59   13.159%   $226.9856   $226.99   $227.00   $227.00  
  Purchase #2 $87.28   8.441%   $94.6473   $94.65   $94.65   $94.60  
  Purchase #3 $243.50   12.166%   $273.1242   $273.12   $273.10   $273.10  
  Purchase #4 $215.45   3.649%   $223.3118   $223.31   $223.30   $223.30  
  Purchase #5 $90.93   13.713%   $103.3992   $103.40   $103.40   $103.40  
  Purchase #6 $9.45   11.325%   $10.5202   $10.52   $10.50   $10.50  
  Purchase #7 $134.93   12.203%   $151.3955   $151.40   $151.40   $151.40  
  7 purchase totals = $982.13       $1,083.3838   $1,083.39   $1,083.35   $1,083.30