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 $86.85   11.733%   $97.0401   $97.04   $97.05   $97.00  
  Purchase #2 $237.88   7.409%   $255.5045   $255.50   $255.50   $255.50  
  Purchase #3 $25.82   7.816%   $27.8381   $27.84   $27.85   $27.80  
  Purchase #4 $119.26   6.461%   $126.9654   $126.97   $126.95   $127.00  
  Purchase #5 $74.99   6.824%   $80.1073   $80.11   $80.10   $80.10  
  Purchase #6 $81.96   10.237%   $90.3502   $90.35   $90.35   $90.40  
  Purchase #7 $192.43   8.284%   $208.3709   $208.37   $208.35   $208.40  
  7 purchase totals = $819.19       $886.1765   $886.18   $886.15   $886.20