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 $105.61   12.722%   $119.0457   $119.05   $119.05   $119.00  
  Purchase #2 $165.93   13.106%   $187.6768   $187.68   $187.70   $187.70  
  Purchase #3 $163.34   8.277%   $176.8597   $176.86   $176.85   $176.90  
  Purchase #4 $56.35   4.486%   $58.8779   $58.88   $58.90   $58.90  
  Purchase #5 $202.96   4.460%   $212.012   $212.01   $212.00   $212.00  
  Purchase #6 $91.86   10.111%   $101.148   $101.15   $101.15   $101.10  
  Purchase #7 $129.28   11.842%   $144.5893   $144.59   $144.60   $144.60  
  7 purchase totals = $915.33       $1,000.2094   $1,000.22   $1,000.25   $1,000.20