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 $54.46   4.243%   $56.7707   $56.77   $56.75   $56.80  
  Purchase #2 $234.97   10.847%   $260.4572   $260.46   $260.45   $260.50  
  Purchase #3 $65.52   9.416%   $71.6894   $71.69   $71.70   $71.70  
  Purchase #4 $180.34   13.626%   $204.9131   $204.91   $204.90   $204.90  
  Purchase #5 $232.52   7.245%   $249.3661   $249.37   $249.35   $249.40  
  Purchase #6 $212.79   10.401%   $234.9223   $234.92   $234.90   $234.90  
  Purchase #7 $117.59   7.200%   $126.0565   $126.06   $126.05   $126.10  
  7 purchase totals = $1,098.19       $1,204.1753   $1,204.18   $1,204.10   $1,204.30