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 $63.53   8.237%   $68.763   $68.76   $68.75   $68.80  
  Purchase #2 $43.45   13.537%   $49.3318   $49.33   $49.35   $49.30  
  Purchase #3 $16.80   5.852%   $17.7831   $17.78   $17.80   $17.80  
  Purchase #4 $172.52   9.829%   $189.477   $189.48   $189.50   $189.50  
  Purchase #5 $231.53   7.821%   $249.638   $249.64   $249.65   $249.60  
  Purchase #6 $25.79   12.313%   $28.9655   $28.97   $28.95   $29.00  
  Purchase #7 $202.66   9.593%   $222.1012   $222.10   $222.10   $222.10  
  7 purchase totals = $756.28       $826.0596   $826.06   $826.10   $826.10