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 $69.66   9.260%   $76.1105   $76.11   $76.10   $76.10  
  Purchase #2 $32.79   5.393%   $34.5584   $34.56   $34.55   $34.60  
  Purchase #3 $206.97   5.869%   $219.1171   $219.12   $219.10   $219.10  
  Purchase #4 $226.52   6.531%   $241.314   $241.31   $241.30   $241.30  
  Purchase #5 $41.65   12.408%   $46.8179   $46.82   $46.80   $46.80  
  Purchase #6 $31.37   12.246%   $35.2116   $35.21   $35.20   $35.20  
  Purchase #7 $182.27   7.744%   $196.385   $196.39   $196.40   $196.40  
  7 purchase totals = $791.23       $849.5145   $849.52   $849.45   $849.50