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 $39.53   11.558%   $44.0989   $44.10   $44.10   $44.10  
  Purchase #2 $244.52   13.839%   $278.3591   $278.36   $278.35   $278.40  
  Purchase #3 $208.45   11.273%   $231.9486   $231.95   $231.95   $231.90  
  Purchase #4 $243.43   3.500%   $251.9501   $251.95   $251.95   $252.00  
  Purchase #5 $202.36   9.546%   $221.6773   $221.68   $221.70   $221.70  
  Purchase #6 $53.28   9.687%   $58.4412   $58.44   $58.45   $58.40  
  Purchase #7 $152.45   4.706%   $159.6243   $159.62   $159.60   $159.60  
  7 purchase totals = $1,144.02       $1,246.0995   $1,246.10   $1,246.10   $1,246.10