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 $13.95   7.250%   $14.9614   $14.96   $14.95   $15.00  
  Purchase #2 $181.46   9.405%   $198.5263   $198.53   $198.55   $198.50  
  Purchase #3 $113.56   12.294%   $127.5211   $127.52   $127.50   $127.50  
  Purchase #4 $61.30   6.579%   $65.3329   $65.33   $65.35   $65.30  
  Purchase #5 $118.69   11.624%   $132.4865   $132.49   $132.50   $132.50  
  Purchase #6 $246.74   10.273%   $272.0876   $272.09   $272.10   $272.10  
  Purchase #7 $239.52   5.371%   $252.3846   $252.38   $252.40   $252.40  
  7 purchase totals = $975.22       $1,063.3004   $1,063.30   $1,063.35   $1,063.30