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 $38.41   12.214%   $43.1014   $43.10   $43.10   $43.10  
  Purchase #2 $116.88   9.850%   $128.3927   $128.39   $128.40   $128.40  
  Purchase #3 $184.77   11.442%   $205.9114   $205.91   $205.90   $205.90  
  Purchase #4 $160.33   3.180%   $165.4285   $165.43   $165.45   $165.40  
  Purchase #5 $236.87   12.111%   $265.5573   $265.56   $265.55   $265.60  
  Purchase #6 $173.70   4.362%   $181.2768   $181.28   $181.30   $181.30  
  Purchase #7 $62.66   10.126%   $69.005   $69.01   $69.00   $69.00  
  7 purchase totals = $973.62       $1,058.6731   $1,058.68   $1,058.70   $1,058.70