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 $246.59   11.632%   $275.2733   $275.27   $275.25   $275.30  
  Purchase #2 $142.52   7.316%   $152.9468   $152.95   $152.95   $152.90  
  Purchase #3 $169.50   6.481%   $180.4853   $180.49   $180.50   $180.50  
  Purchase #4 $55.55   9.783%   $60.9845   $60.98   $61.00   $61.00  
  Purchase #5 $95.76   7.400%   $102.8462   $102.85   $102.85   $102.80  
  Purchase #6 $192.27   9.215%   $209.9877   $209.99   $210.00   $210.00  
  Purchase #7 $157.82   10.835%   $174.9198   $174.92   $174.90   $174.90  
  7 purchase totals = $1,060.01       $1,157.4436   $1,157.45   $1,157.45   $1,157.40