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 $56.85   5.270%   $59.846   $59.85   $59.85   $59.80  
  Purchase #2 $142.27   13.413%   $161.3527   $161.35   $161.35   $161.40  
  Purchase #3 $239.97   12.844%   $270.7917   $270.79   $270.80   $270.80  
  Purchase #4 $84.89   6.432%   $90.3501   $90.35   $90.35   $90.40  
  Purchase #5 $22.95   8.721%   $24.9515   $24.95   $24.95   $25.00  
  Purchase #6 $192.68   6.403%   $205.0173   $205.02   $205.00   $205.00  
  Purchase #7 $59.92   3.426%   $61.9729   $61.97   $61.95   $62.00  
  7 purchase totals = $799.53       $874.2822   $874.28   $874.25   $874.40