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 $160.58   8.565%   $174.3337   $174.33   $174.35   $174.30  
  Purchase #2 $124.52   8.577%   $135.2001   $135.20   $135.20   $135.20  
  Purchase #3 $150.68   3.318%   $155.6796   $155.68   $155.70   $155.70  
  Purchase #4 $112.42   13.822%   $127.9587   $127.96   $127.95   $128.00  
  Purchase #5 $69.28   12.144%   $77.6934   $77.69   $77.70   $77.70  
  Purchase #6 $186.35   8.341%   $201.8935   $201.89   $201.90   $201.90  
  Purchase #7 $157.70   8.843%   $171.6454   $171.65   $171.65   $171.60  
  7 purchase totals = $961.53       $1,044.4044   $1,044.40   $1,044.45   $1,044.40