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 $84.75   11.818%   $94.7658   $94.77   $94.75   $94.80  
  Purchase #2 $221.56   6.418%   $235.7797   $235.78   $235.80   $235.80  
  Purchase #3 $86.76   3.273%   $89.5997   $89.60   $89.60   $89.60  
  Purchase #4 $192.78   9.162%   $210.4425   $210.44   $210.45   $210.40  
  Purchase #5 $83.35   9.612%   $91.3616   $91.36   $91.35   $91.40  
  Purchase #6 $205.65   5.844%   $217.6682   $217.67   $217.65   $217.70  
  Purchase #7 $170.98   3.145%   $176.3573   $176.36   $176.35   $176.40  
  7 purchase totals = $1,045.83       $1,115.9748   $1,115.98   $1,115.95   $1,116.10