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 $185.61   8.832%   $202.0031   $202.00   $202.00   $202.00  
  Purchase #2 $102.67   7.651%   $110.5253   $110.53   $110.55   $110.50  
  Purchase #3 $71.97   5.709%   $76.0788   $76.08   $76.10   $76.10  
  Purchase #4 $137.94   10.767%   $152.792   $152.79   $152.80   $152.80  
  Purchase #5 $196.54   7.367%   $211.0191   $211.02   $211.00   $211.00  
  Purchase #6 $183.65   3.365%   $189.8298   $189.83   $189.85   $189.80  
  Purchase #7 $49.72   12.660%   $56.0146   $56.01   $56.00   $56.00  
  7 purchase totals = $928.10       $998.2627   $998.26   $998.30   $998.20