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 $229.65   7.224%   $246.2399   $246.24   $246.25   $246.20  
  Purchase #2 $119.93   12.851%   $135.3422   $135.34   $135.35   $135.30  
  Purchase #3 $179.54   7.737%   $193.431   $193.43   $193.45   $193.40  
  Purchase #4 $179.34   6.774%   $191.4885   $191.49   $191.50   $191.50  
  Purchase #5 $172.49   4.206%   $179.7449   $179.74   $179.75   $179.70  
  Purchase #6 $39.81   9.163%   $43.4578   $43.46   $43.45   $43.50  
  Purchase #7 $15.34   11.360%   $17.0826   $17.08   $17.10   $17.10  
  7 purchase totals = $936.10       $1,006.7869   $1,006.78   $1,006.85   $1,006.70