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 $206.61   8.539%   $224.2524   $224.25   $224.25   $224.30  
  Purchase #2 $101.97   10.240%   $112.4117   $112.41   $112.40   $112.40  
  Purchase #3 $39.26   9.718%   $43.0753   $43.08   $43.10   $43.10  
  Purchase #4 $237.99   4.327%   $248.2878   $248.29   $248.30   $248.30  
  Purchase #5 $139.57   8.304%   $151.1599   $151.16   $151.15   $151.20  
  Purchase #6 $198.83   6.160%   $211.0779   $211.08   $211.10   $211.10  
  Purchase #7 $235.29   12.308%   $264.2495   $264.25   $264.25   $264.20  
  7 purchase totals = $1,159.52       $1,254.5145   $1,254.52   $1,254.55   $1,254.60