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 $24.37   13.646%   $27.6955   $27.70   $27.70   $27.70  
  Purchase #2 $211.60   6.487%   $225.3265   $225.33   $225.35   $225.30  
  Purchase #3 $164.74   5.369%   $173.5849   $173.58   $173.60   $173.60  
  Purchase #4 $232.75   4.493%   $243.2075   $243.21   $243.20   $243.20  
  Purchase #5 $51.53   4.325%   $53.7587   $53.76   $53.75   $53.80  
  Purchase #6 $151.92   3.483%   $157.2114   $157.21   $157.20   $157.20  
  Purchase #7 $189.82   6.512%   $202.1811   $202.18   $202.20   $202.20  
  7 purchase totals = $1,026.73       $1,082.9656   $1,082.97   $1,083.00   $1,083.00