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 $32.51   12.694%   $36.6368   $36.64   $36.65   $36.60  
  Purchase #2 $215.37   10.102%   $237.1267   $237.13   $237.15   $237.10  
  Purchase #3 $159.29   4.417%   $166.3258   $166.33   $166.35   $166.30  
  Purchase #4 $127.32   9.584%   $139.5223   $139.52   $139.50   $139.50  
  Purchase #5 $198.77   13.271%   $225.1488   $225.15   $225.15   $225.10  
  Purchase #6 $160.99   4.168%   $167.7001   $167.70   $167.70   $167.70  
  Purchase #7 $36.80   12.845%   $41.527   $41.53   $41.55   $41.50  
  7 purchase totals = $931.05       $1,013.9875   $1,014.00   $1,014.05   $1,013.80