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 $186.57   10.303%   $205.7923   $205.79   $205.80   $205.80  
  Purchase #2 $153.94   8.568%   $167.1296   $167.13   $167.15   $167.10  
  Purchase #3 $80.69   3.497%   $83.5117   $83.51   $83.50   $83.50  
  Purchase #4 $116.87   13.267%   $132.3751   $132.38   $132.40   $132.40  
  Purchase #5 $24.29   9.149%   $26.5123   $26.51   $26.50   $26.50  
  Purchase #6 $150.68   11.212%   $167.5742   $167.57   $167.55   $167.60  
  Purchase #7 $41.60   4.369%   $43.4175   $43.42   $43.40   $43.40  
  7 purchase totals = $754.64       $826.3127   $826.31   $826.30   $826.30