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 $202.57   11.814%   $226.5016   $226.50   $226.50   $226.50  
  Purchase #2 $62.60   4.736%   $65.5647   $65.56   $65.55   $65.60  
  Purchase #3 $70.52   4.589%   $73.7562   $73.76   $73.75   $73.80  
  Purchase #4 $67.36   9.386%   $73.6824   $73.68   $73.70   $73.70  
  Purchase #5 $79.82   5.226%   $83.9914   $83.99   $84.00   $84.00  
  Purchase #6 $237.30   11.572%   $264.7604   $264.76   $264.75   $264.80  
  Purchase #7 $42.93   10.827%   $47.578   $47.58   $47.60   $47.60  
  7 purchase totals = $763.10       $835.8347   $835.83   $835.85   $836.00