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 $145.67   12.361%   $163.6763   $163.68   $163.70   $163.70  
  Purchase #2 $177.74   9.713%   $195.0039   $195.00   $195.00   $195.00  
  Purchase #3 $47.99   5.390%   $50.5767   $50.58   $50.60   $50.60  
  Purchase #4 $9.45   5.559%   $9.9753   $9.98   $10.00   $10.00  
  Purchase #5 $120.71   11.385%   $134.4528   $134.45   $134.45   $134.50  
  Purchase #6 $168.61   10.623%   $186.5214   $186.52   $186.50   $186.50  
  Purchase #7 $234.27   9.189%   $255.7971   $255.80   $255.80   $255.80  
  7 purchase totals = $904.44       $996.0035   $996.01   $996.05   $996.10