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 $129.27   13.755%   $147.0511   $147.05   $147.05   $147.10  
  Purchase #2 $240.33   11.206%   $267.2614   $267.26   $267.25   $267.30  
  Purchase #3 $55.91   12.216%   $62.74   $62.74   $62.75   $62.70  
  Purchase #4 $167.52   8.242%   $181.327   $181.33   $181.35   $181.30  
  Purchase #5 $183.66   10.804%   $203.5026   $203.50   $203.50   $203.50  
  Purchase #6 $47.27   12.234%   $53.053   $53.05   $53.05   $53.10  
  Purchase #7 $32.49   4.194%   $33.8526   $33.85   $33.85   $33.90  
  7 purchase totals = $856.45       $948.7877   $948.78   $948.80   $948.90