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 $246.44   11.839%   $275.616   $275.62   $275.60   $275.60  
  Purchase #2 $146.39   3.395%   $151.3599   $151.36   $151.35   $151.40  
  Purchase #3 $180.51   12.713%   $203.4582   $203.46   $203.45   $203.50  
  Purchase #4 $182.31   9.512%   $199.6513   $199.65   $199.65   $199.70  
  Purchase #5 $24.76   3.469%   $25.6189   $25.62   $25.60   $25.60  
  Purchase #6 $47.32   3.860%   $49.1466   $49.15   $49.15   $49.10  
  Purchase #7 $201.82   4.487%   $210.8757   $210.88   $210.90   $210.90  
  7 purchase totals = $1,029.55       $1,115.7266   $1,115.74   $1,115.70   $1,115.80