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 $75.78   11.457%   $84.4621   $84.46   $84.45   $84.50  
  Purchase #2 $230.59   3.776%   $239.2971   $239.30   $239.30   $239.30  
  Purchase #3 $152.34   11.155%   $169.3335   $169.33   $169.35   $169.30  
  Purchase #4 $235.60   4.156%   $245.3915   $245.39   $245.40   $245.40  
  Purchase #5 $182.77   9.615%   $200.3433   $200.34   $200.35   $200.30  
  Purchase #6 $92.76   11.163%   $103.1148   $103.11   $103.10   $103.10  
  Purchase #7 $202.68   8.714%   $220.3415   $220.34   $220.35   $220.30  
  7 purchase totals = $1,172.52       $1,262.2838   $1,262.27   $1,262.30   $1,262.20