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 $48.82   12.157%   $54.755   $54.76   $54.75   $54.80  
  Purchase #2 $22.52   5.520%   $23.7631   $23.76   $23.75   $23.80  
  Purchase #3 $134.47   8.523%   $145.9309   $145.93   $145.95   $145.90  
  Purchase #4 $118.93   7.112%   $127.3883   $127.39   $127.40   $127.40  
  Purchase #5 $184.40   9.790%   $202.4528   $202.45   $202.45   $202.50  
  Purchase #6 $135.97   11.608%   $151.7534   $151.75   $151.75   $151.80  
  Purchase #7 $217.66   7.870%   $234.7898   $234.79   $234.80   $234.80  
  7 purchase totals = $862.77       $940.8333   $940.83   $940.85   $941.00