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 $34.57   7.132%   $37.0355   $37.04   $37.05   $37.00  
  Purchase #2 $6.90   4.433%   $7.2059   $7.21   $7.20   $7.20  
  Purchase #3 $156.80   4.547%   $163.9297   $163.93   $163.95   $163.90  
  Purchase #4 $166.34   6.873%   $177.7725   $177.77   $177.75   $177.80  
  Purchase #5 $88.66   6.209%   $94.1649   $94.16   $94.15   $94.20  
  Purchase #6 $191.62   10.771%   $212.2594   $212.26   $212.25   $212.30  
  Purchase #7 $202.54   3.270%   $209.1631   $209.16   $209.15   $209.20  
  7 purchase totals = $847.43       $901.5310   $901.53   $901.50   $901.60