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 $228.69   9.837%   $251.1862   $251.19   $251.20   $251.20  
  Purchase #2 $68.72   11.866%   $76.8743   $76.87   $76.85   $76.90  
  Purchase #3 $160.50   11.692%   $179.2657   $179.27   $179.25   $179.30  
  Purchase #4 $110.38   4.384%   $115.2191   $115.22   $115.20   $115.20  
  Purchase #5 $244.66   6.124%   $259.643   $259.64   $259.65   $259.60  
  Purchase #6 $59.65   9.477%   $65.303   $65.30   $65.30   $65.30  
  Purchase #7 $181.46   12.307%   $203.7923   $203.79   $203.80   $203.80  
  7 purchase totals = $1,054.06       $1,151.2836   $1,151.28   $1,151.25   $1,151.30