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 $90.76   6.173%   $96.3626   $96.36   $96.35   $96.40  
  Purchase #2 $166.96   6.244%   $177.385   $177.39   $177.40   $177.40  
  Purchase #3 $71.75   3.366%   $74.1651   $74.17   $74.15   $74.20  
  Purchase #4 $51.37   8.580%   $55.7775   $55.78   $55.80   $55.80  
  Purchase #5 $203.76   11.579%   $227.3534   $227.35   $227.35   $227.40  
  Purchase #6 $83.41   11.194%   $92.7469   $92.75   $92.75   $92.70  
  Purchase #7 $116.28   4.640%   $121.6754   $121.68   $121.70   $121.70  
  7 purchase totals = $784.29       $845.4659   $845.48   $845.50   $845.60