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 $126.58   7.404%   $135.952   $135.95   $135.95   $136.00  
  Purchase #2 $56.48   8.562%   $61.3158   $61.32   $61.30   $61.30  
  Purchase #3 $70.35   4.693%   $73.6515   $73.65   $73.65   $73.70  
  Purchase #4 $167.33   4.862%   $175.4656   $175.47   $175.45   $175.50  
  Purchase #5 $160.47   7.684%   $172.8005   $172.80   $172.80   $172.80  
  Purchase #6 $172.47   6.108%   $183.0045   $183.00   $183.00   $183.00  
  Purchase #7 $247.29   3.822%   $256.7414   $256.74   $256.75   $256.70  
  7 purchase totals = $1,000.97       $1,058.9313   $1,058.93   $1,058.90   $1,059.00