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 $49.52   9.629%   $54.2883   $54.29   $54.30   $54.30  
  Purchase #2 $195.65   6.297%   $207.9701   $207.97   $207.95   $208.00  
  Purchase #3 $160.29   5.749%   $169.5051   $169.51   $169.50   $169.50  
  Purchase #4 $19.79   9.143%   $21.5994   $21.60   $21.60   $21.60  
  Purchase #5 $53.98   5.266%   $56.8226   $56.82   $56.80   $56.80  
  Purchase #6 $188.83   6.533%   $201.1663   $201.17   $201.15   $201.20  
  Purchase #7 $231.36   10.530%   $255.7222   $255.72   $255.70   $255.70  
  7 purchase totals = $899.42       $967.0740   $967.08   $967.00   $967.10