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 $245.50   9.137%   $267.9313   $267.93   $267.95   $267.90  
  Purchase #2 $228.72   13.308%   $259.1581   $259.16   $259.15   $259.20  
  Purchase #3 $197.70   5.331%   $208.2394   $208.24   $208.25   $208.20  
  Purchase #4 $91.29   3.813%   $94.7709   $94.77   $94.75   $94.80  
  Purchase #5 $56.59   3.455%   $58.5452   $58.55   $58.55   $58.50  
  Purchase #6 $72.80   11.314%   $81.0366   $81.04   $81.05   $81.00  
  Purchase #7 $85.97   6.458%   $91.5219   $91.52   $91.50   $91.50  
  7 purchase totals = $978.57       $1,061.2034   $1,061.21   $1,061.20   $1,061.10