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 $248.46   10.817%   $275.3359   $275.34   $275.35   $275.30  
  Purchase #2 $211.98   4.212%   $220.9086   $220.91   $220.90   $220.90  
  Purchase #3 $13.82   4.247%   $14.4069   $14.41   $14.40   $14.40  
  Purchase #4 $81.29   5.192%   $85.5106   $85.51   $85.50   $85.50  
  Purchase #5 $78.93   11.593%   $88.0804   $88.08   $88.10   $88.10  
  Purchase #6 $191.62   5.542%   $202.2396   $202.24   $202.25   $202.20  
  Purchase #7 $149.88   11.862%   $167.6588   $167.66   $167.65   $167.70  
  7 purchase totals = $975.98       $1,054.1408   $1,054.15   $1,054.15   $1,054.10