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 $84.86   9.599%   $93.0057   $93.01   $93.00   $93.00  
  Purchase #2 $91.29   11.255%   $101.5647   $101.56   $101.55   $101.60  
  Purchase #3 $59.27   11.626%   $66.1607   $66.16   $66.15   $66.20  
  Purchase #4 $249.30   13.606%   $283.2198   $283.22   $283.20   $283.20  
  Purchase #5 $212.64   5.444%   $224.2161   $224.22   $224.20   $224.20  
  Purchase #6 $209.55   13.277%   $237.372   $237.37   $237.35   $237.40  
  Purchase #7 $22.58   5.493%   $23.8203   $23.82   $23.80   $23.80  
  7 purchase totals = $929.49       $1,029.3593   $1,029.36   $1,029.25   $1,029.40