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 $59.88   6.729%   $63.9093   $63.91   $63.90   $63.90  
  Purchase #2 $47.87   12.871%   $54.0313   $54.03   $54.05   $54.00  
  Purchase #3 $116.95   9.662%   $128.2497   $128.25   $128.25   $128.20  
  Purchase #4 $240.64   11.364%   $267.9863   $267.99   $268.00   $268.00  
  Purchase #5 $241.27   6.634%   $257.2759   $257.28   $257.30   $257.30  
  Purchase #6 $180.74   11.728%   $201.9372   $201.94   $201.95   $201.90  
  Purchase #7 $239.57   6.622%   $255.4343   $255.43   $255.45   $255.40  
  7 purchase totals = $1,126.92       $1,228.8240   $1,228.83   $1,228.90   $1,228.70