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 $49.57   8.282%   $53.6754   $53.68   $53.70   $53.70  
  Purchase #2 $209.76   9.172%   $228.9992   $229.00   $229.00   $229.00  
  Purchase #3 $82.86   3.108%   $85.4353   $85.44   $85.45   $85.40  
  Purchase #4 $170.53   7.240%   $182.8764   $182.88   $182.90   $182.90  
  Purchase #5 $161.65   7.787%   $174.2377   $174.24   $174.25   $174.20  
  Purchase #6 $184.26   9.808%   $202.3322   $202.33   $202.35   $202.30  
  Purchase #7 $115.75   12.777%   $130.5394   $130.54   $130.55   $130.50  
  7 purchase totals = $974.38       $1,058.0956   $1,058.11   $1,058.20   $1,058.00