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 $236.80   11.810%   $264.7661   $264.77   $264.75   $264.80  
  Purchase #2 $169.88   4.275%   $177.1424   $177.14   $177.15   $177.10  
  Purchase #3 $216.66   8.510%   $235.0978   $235.10   $235.10   $235.10  
  Purchase #4 $11.92   3.519%   $12.3395   $12.34   $12.35   $12.30  
  Purchase #5 $208.93   11.487%   $232.9298   $232.93   $232.95   $232.90  
  Purchase #6 $21.33   3.701%   $22.1194   $22.12   $22.10   $22.10  
  Purchase #7 $118.56   7.121%   $127.0027   $127.00   $127.00   $127.00  
  7 purchase totals = $984.08       $1,071.3977   $1,071.40   $1,071.40   $1,071.30