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 $54.52   12.115%   $61.1251   $61.13   $61.15   $61.10  
  Purchase #2 $163.27   11.769%   $182.4852   $182.49   $182.50   $182.50  
  Purchase #3 $152.70   13.656%   $173.5527   $173.55   $173.55   $173.60  
  Purchase #4 $229.86   10.717%   $254.4941   $254.49   $254.50   $254.50  
  Purchase #5 $177.61   6.698%   $189.5063   $189.51   $189.50   $189.50  
  Purchase #6 $81.30   7.735%   $87.5886   $87.59   $87.60   $87.60  
  Purchase #7 $33.50   13.451%   $38.0061   $38.01   $38.00   $38.00  
  7 purchase totals = $892.76       $986.7581   $986.77   $986.80   $986.80