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 $100.41   9.749%   $110.199   $110.20   $110.20   $110.20  
  Purchase #2 $5.42   4.571%   $5.6677   $5.67   $5.65   $5.70  
  Purchase #3 $48.47   8.427%   $52.5546   $52.55   $52.55   $52.60  
  Purchase #4 $10.52   3.182%   $10.8547   $10.85   $10.85   $10.90  
  Purchase #5 $90.55   11.272%   $100.7568   $100.76   $100.75   $100.80  
  Purchase #6 $8.57   5.319%   $9.0258   $9.03   $9.05   $9.00  
  Purchase #7 $7.57   11.738%   $8.4586   $8.46   $8.45   $8.50  
  7 purchase totals = $271.51       $297.5172   $297.52   $297.50   $297.70