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 $218.95   12.813%   $247.0041   $247.00   $247.00   $247.00  
  Purchase #2 $122.25   10.203%   $134.7232   $134.72   $134.70   $134.70  
  Purchase #3 $198.50   6.733%   $211.865   $211.87   $211.85   $211.90  
  Purchase #4 $125.92   13.645%   $143.1018   $143.10   $143.10   $143.10  
  Purchase #5 $80.84   8.453%   $87.6734   $87.67   $87.65   $87.70  
  Purchase #6 $144.67   7.418%   $155.4016   $155.40   $155.40   $155.40  
  Purchase #7 $241.95   5.203%   $254.5387   $254.54   $254.55   $254.50  
  7 purchase totals = $1,133.08       $1,234.3078   $1,234.30   $1,234.25   $1,234.30