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 $184.69   9.167%   $201.6205   $201.62   $201.60   $201.60  
  Purchase #2 $25.86   12.110%   $28.9916   $28.99   $29.00   $29.00  
  Purchase #3 $196.29   8.278%   $212.5389   $212.54   $212.55   $212.50  
  Purchase #4 $52.34   3.804%   $54.331   $54.33   $54.35   $54.30  
  Purchase #5 $157.55   4.826%   $165.1534   $165.15   $165.15   $165.20  
  Purchase #6 $64.71   10.685%   $71.6243   $71.62   $71.60   $71.60  
  Purchase #7 $220.85   10.376%   $243.7654   $243.77   $243.75   $243.80  
  7 purchase totals = $902.29       $978.0251   $978.02   $978.00   $978.00