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 $227.30   8.470%   $246.5523   $246.55   $246.55   $246.60  
  Purchase #2 $87.41   7.685%   $94.1275   $94.13   $94.15   $94.10  
  Purchase #3 $17.32   11.641%   $19.3362   $19.34   $19.35   $19.30  
  Purchase #4 $43.93   6.770%   $46.9041   $46.90   $46.90   $46.90  
  Purchase #5 $27.79   6.235%   $29.5227   $29.52   $29.50   $29.50  
  Purchase #6 $111.90   10.578%   $123.7368   $123.74   $123.75   $123.70  
  Purchase #7 $218.46   11.777%   $244.188   $244.19   $244.20   $244.20  
  7 purchase totals = $734.11       $804.3676   $804.37   $804.40   $804.30