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 $173.96   5.350%   $183.2669   $183.27   $183.25   $183.30  
  Purchase #2 $16.39   4.232%   $17.0836   $17.08   $17.10   $17.10  
  Purchase #3 $206.37   6.787%   $220.3763   $220.38   $220.40   $220.40  
  Purchase #4 $68.46   9.807%   $75.1739   $75.17   $75.15   $75.20  
  Purchase #5 $208.50   9.718%   $228.762   $228.76   $228.75   $228.80  
  Purchase #6 $112.44   12.827%   $126.8627   $126.86   $126.85   $126.90  
  Purchase #7 $151.26   13.742%   $172.0461   $172.05   $172.05   $172.00  
  7 purchase totals = $937.38       $1,023.5715   $1,023.57   $1,023.55   $1,023.70