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 $189.76   3.316%   $196.0524   $196.05   $196.05   $196.10  
  Purchase #2 $202.42   7.383%   $217.3647   $217.36   $217.35   $217.40  
  Purchase #3 $65.52   12.353%   $73.6137   $73.61   $73.60   $73.60  
  Purchase #4 $116.76   11.365%   $130.0298   $130.03   $130.05   $130.00  
  Purchase #5 $218.56   12.177%   $245.1741   $245.17   $245.15   $245.20  
  Purchase #6 $195.67   12.381%   $219.8959   $219.90   $219.90   $219.90  
  Purchase #7 $110.42   9.840%   $121.2853   $121.29   $121.30   $121.30  
  7 purchase totals = $1,099.11       $1,203.4159   $1,203.41   $1,203.40   $1,203.50