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 $227.43   3.195%   $234.6964   $234.70   $234.70   $234.70  
  Purchase #2 $90.44   3.408%   $93.5222   $93.52   $93.50   $93.50  
  Purchase #3 $12.33   13.654%   $14.0135   $14.01   $14.00   $14.00  
  Purchase #4 $203.50   5.830%   $215.3641   $215.36   $215.35   $215.40  
  Purchase #5 $213.27   6.185%   $226.4607   $226.46   $226.45   $226.50  
  Purchase #6 $47.32   6.518%   $50.4043   $50.40   $50.40   $50.40  
  Purchase #7 $156.50   6.850%   $167.2203   $167.22   $167.20   $167.20  
  7 purchase totals = $950.79       $1,001.6815   $1,001.67   $1,001.60   $1,001.70