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 $220.95   12.816%   $249.267   $249.27   $249.25   $249.30  
  Purchase #2 $204.25   9.790%   $224.2461   $224.25   $224.25   $224.20  
  Purchase #3 $53.48   4.714%   $56.001   $56.00   $56.00   $56.00  
  Purchase #4 $213.39   10.106%   $234.9552   $234.96   $234.95   $235.00  
  Purchase #5 $146.48   6.132%   $155.4622   $155.46   $155.45   $155.50  
  Purchase #6 $12.74   9.592%   $13.962   $13.96   $13.95   $14.00  
  Purchase #7 $74.81   7.402%   $80.3474   $80.35   $80.35   $80.30  
  7 purchase totals = $926.10       $1,014.2409   $1,014.25   $1,014.20   $1,014.30