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 $217.86   13.113%   $246.428   $246.43   $246.45   $246.40  
  Purchase #2 $96.68   5.847%   $102.3329   $102.33   $102.35   $102.30  
  Purchase #3 $183.31   13.333%   $207.7507   $207.75   $207.75   $207.80  
  Purchase #4 $147.57   4.162%   $153.7119   $153.71   $153.70   $153.70  
  Purchase #5 $53.78   5.362%   $56.6637   $56.66   $56.65   $56.70  
  Purchase #6 $179.31   4.525%   $187.4238   $187.42   $187.40   $187.40  
  Purchase #7 $32.92   4.405%   $34.3701   $34.37   $34.35   $34.40  
  7 purchase totals = $911.43       $988.6811   $988.67   $988.65   $988.70