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 $174.77   10.307%   $192.7835   $192.78   $192.80   $192.80  
  Purchase #2 $60.93   3.336%   $62.9626   $62.96   $62.95   $63.00  
  Purchase #3 $161.80   9.600%   $177.3328   $177.33   $177.35   $177.30  
  Purchase #4 $228.40   3.139%   $235.5695   $235.57   $235.55   $235.60  
  Purchase #5 $241.68   5.498%   $254.9676   $254.97   $254.95   $255.00  
  Purchase #6 $238.83   3.313%   $246.7424   $246.74   $246.75   $246.70  
  Purchase #7 $57.31   5.414%   $60.4128   $60.41   $60.40   $60.40  
  7 purchase totals = $1,163.72       $1,230.7712   $1,230.76   $1,230.75   $1,230.80