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 $153.66   7.751%   $165.5702   $165.57   $165.55   $165.60  
  Purchase #2 $232.57   6.629%   $247.9871   $247.99   $248.00   $248.00  
  Purchase #3 $145.98   12.442%   $164.1428   $164.14   $164.15   $164.10  
  Purchase #4 $21.61   6.399%   $22.9928   $22.99   $23.00   $23.00  
  Purchase #5 $197.92   11.461%   $220.6036   $220.60   $220.60   $220.60  
  Purchase #6 $60.99   5.612%   $64.4128   $64.41   $64.40   $64.40  
  Purchase #7 $153.96   10.611%   $170.2967   $170.30   $170.30   $170.30  
  7 purchase totals = $966.69       $1,056.0060   $1,056.00   $1,056.00   $1,056.00