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 $22.55   10.693%   $24.9613   $24.96   $24.95   $25.00  
  Purchase #2 $114.77   3.448%   $118.7273   $118.73   $118.75   $118.70  
  Purchase #3 $205.27   5.759%   $217.0915   $217.09   $217.10   $217.10  
  Purchase #4 $161.33   11.225%   $179.4393   $179.44   $179.45   $179.40  
  Purchase #5 $150.84   6.419%   $160.5224   $160.52   $160.50   $160.50  
  Purchase #6 $70.79   3.325%   $73.1438   $73.14   $73.15   $73.10  
  Purchase #7 $223.91   9.567%   $245.3315   $245.33   $245.35   $245.30  
  7 purchase totals = $949.46       $1,019.2171   $1,019.21   $1,019.25   $1,019.10