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 $202.29   4.417%   $211.2251   $211.23   $211.25   $211.20  
  Purchase #2 $144.80   11.606%   $161.6055   $161.61   $161.60   $161.60  
  Purchase #3 $167.38   10.579%   $185.0871   $185.09   $185.10   $185.10  
  Purchase #4 $58.77   11.198%   $65.3511   $65.35   $65.35   $65.40  
  Purchase #5 $245.79   9.843%   $269.9831   $269.98   $270.00   $270.00  
  Purchase #6 $138.56   10.797%   $153.5203   $153.52   $153.50   $153.50  
  Purchase #7 $10.41   12.680%   $11.73   $11.73   $11.75   $11.70  
  7 purchase totals = $968.00       $1,058.5022   $1,058.51   $1,058.55   $1,058.50